Display device

ABSTRACT

To provide a display device having a high contrast ratio by a simple and easy method and to manufacture a high-performance display device at low cost, in a display device having a display element between a pair of light-transmitting substrates, layers each including a polarizer having different wavelength distribution of extinction coefficient from each other with respect to the absorption axes are stacked and provided on an outer side of the light-transmitting substrates. Further, a retardation plate may be provided between the stacked polarizers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a display device havinga polarizer.

2. Description of the Related Art

A so-called flat panel display, which is a display device that is verythin and lightweight as compared to the conventional cathode-ray tubedisplay device, has been developed. A liquid crystal display devicehaving a liquid crystal element as a display element, a light emittingdevice having a self-light emitting element, an FED (field emissiondisplay) using an electron beam, and the like compete in the market offlat panel displays. Therefore, lower power consumption and a highercontrast ratio are demanded to increase the added value so as todifferentiate from other products.

In general, in a liquid crystal display device, each substrate isprovided with one polarizing plate to keep a contrast ratio. Whendisplay of darker black is performed, the contrast ratio can beincreased accordingly. Thus, higher display quality can be provided whenan image is seen in a dark room such as a home theater room.

For example, in order to reduce display nonuniformity caused due toshortage of polarization degree and polarization distribution ofpolarizing plates and to improve a contrast ratio, a structure issuggested in which a first polarizing plate is provided outside asubstrate on a viewing side of a liquid crystal cell, a secondpolarizing plate is provided outside a substrate on a side opposite tothe viewing side, and a third polarizing plate is provided forincreasing the degree of polarization when light from an auxiliary lightsource provided on the substrate side opposite to the viewing side ispolarized through the second polarizing plate and transmitted throughthe liquid crystal cell (see Reference 1: PCT International PublicationNo. 00/34821).

SUMMARY OF THE INVENTION

However, a yet higher contrast ratio has been demanded to be enhancedand researches have been made for enhancement in contrast ratio ofliquid crystal display devices. Further, there is a problem in that apolarizing plate having a higher degree of polarization is expensive.

A method for improving a contrast ratio by using three polarizing platesas described in Reference 1 can be realized by using an inexpensivepolarizing plate; however, it is difficult to perform display with ahigher contrast ratio by the method. Further, the dependence ofabsorption properties of a polarizer on a wavelength is not constant,that is, the polarizer has properties of hardly absorbing light of thecertain wavelength region. Accordingly, even when a plurality ofpolarizers of the same type is used in attempting to improve contrastratio, a certain wavelength region of light which is hardly absorbedremains. This causes slight light leakage, and the light leakageprevents a contrast ratio from being enhanced.

In view of the aforementioned problems, an object of the invention is toprovide a display device having a high contrast ratio by a simple andeasy method. Another object of the invention is to manufacture ahigh-performance display device at low cost.

It is a feature of the present invention that at least one oflight-transmitting substrates which are provided to face each other isprovided with a layer including stacked polarizers, and the stackedpolarizers have different wavelength distributions of extinctioncoefficients and are arranged so that their absorption axes are deviatedfrom a parallel Nicols state. Further, a wave plate or a retardationplate may be provided between the stacked polarizers.

A polarizer has an absorption axis, and when polarizers are stacked, astate where the absorption axes of the polarizers are parallel to eachother is referred to as a parallel Nicols state, while a state where theabsorption axes of the polarizers are perpendicular to each other isreferred to as a crossed Nicols state. Note that a polarizercharacteristically has a transmission axis perpendicular to theabsorption axis. Therefore, a state where the transmission axes areparallel to each other can also be referred to as a parallel Nicolsstate, and a state where transmission axes are perpendicular to eachother can also be referred to as a crossed Nicols state.

Further, a polarizer has a specific light extinction coefficient. Thisis because the dependence of the absorption properties of a polarizer ona wavelength is not constant, and the absorption properties with respectto a certain wavelength region are lower than that with respective toanother wavelength region, that is, the polarizer has properties ofhardly absorbing light of the certain wavelength region. In the presentinvention, the absorption axes of stacked polarizers have differentwavelength distributions of extinction coefficients.

The wavelength region of light which is hardly absorbed can beeliminated or reduced by combining and stacking polarizers havingdifferent wavelength distributions of extinction coefficients withrespect to the absorption axes. Thus, even slight light leakage can beprevented and contrast ratio can be further improved.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and layers including stacked polarizers onan outer side of the first light-transmitting substrate and the secondlight-transmitting substrate. The stacked polarizers have differentwavelength distributions of extinction coefficients with respect toabsorption axes, and the stacked polarizers are arranged so that theirabsorption axes are deviated from a parallel Nicols state.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and layers including stacked polarizers onan outer side of the first light-transmitting substrate and the secondlight-transmitting substrate; and a retardation plate provided betweenthe layers including the stacked polarizers and the firstlight-transmitting substrate and the second light-transmitting substraterespectively. The stacked polarizers have different wavelengthdistributions of extinction coefficients with respect to absorptionaxes, and the stacked polarizers are arranged so that their absorptionaxes are deviated from a parallel Nicols state.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and a first layer including first stackedpolarizers on an outer side of the first light-transmitting substrate;and a second layer including second stacked polarizers on an outer sideof the second light-transmitting substrate. The first stacked polarizershave different wavelength distributions of extinction coefficients withrespect to absorption axes, the second stacked polarizers have differentwavelength distributions of extinction coefficients with respect toabsorption axes, the first stacked polarizers are arranged so that theirabsorption axes are deviated from a parallel Nicols state, and thesecond stacked polarizers are arranged so that their absorption axes aredeviated from a parallel Nicols state.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and a first layer including first stackedpolarizers on an outer side of the first light-transmitting substrate; asecond layer including second stacked polarizers on an outer side of thesecond light-transmitting substrate; a first retardation plate betweenthe first layer including the first stacked polarizers and the firstlight-transmitting substrate; and a second retardation plate between thesecond layer including the second stacked polarizers and the secondlight-transmitting substrate. The first stacked polarizers havedifferent wavelength distributions of extinction coefficients withrespect to absorption axes, the second stacked polarizers have differentwavelength distributions of extinction coefficients with respect toabsorption axes, the first stacked polarizers are arranged so that theirabsorption axes are deviated from a parallel Nicols state, and thesecond stacked polarizers are arranged so that their absorption axes aredeviated from a parallel Nicols state.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and a first layer including first stackedpolarizers on an outer side of the first light-transmitting substrate;and a second layer including second stacked polarizers on an outer sideof the second light-transmitting substrate. The first stacked polarizershave different wavelength distributions of extinction coefficients withrespect to absorption axes, the second stacked polarizers have differentwavelength distributions of extinction coefficients from each other withrespect to absorption axes, the first stacked polarizers are arranged sothat their absorption axes are deviated from a parallel Nicols state,the second stacked polarizers are arranged so that their absorption axesare deviated from a parallel Nicols state, the first layer including thefirst stacked polarizers has a first polarizer and a second polarizerwhich are sequentially stacked from the first light-transmittingsubstrate side, and the first stacked polarizers and the second stackedpolarizers are arranged so that their absorption axes are in a crossedNicols state.

A mode of a display device the present invention includes a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; and a first layer including first stackedpolarizers on an outer side of the first light-transmitting substrate; asecond layer including second stacked polarizers on an outer side of thesecond light-transmitting substrate; a first retardation plate betweenthe first light-transmitting substrate and the first layer including thefirst stacked polarizers; and a second retardation plate between thesecond light-transmitting substrate and the second layer including thesecond stacked polarizers. The first stacked polarizers have differentwavelength distributions of extinction coefficients from each other withrespect to absorption axes, the second stacked polarizers have differentwavelength distributions of extinction coefficients from each other withrespect to absorption axes, the first stacked polarizers are arranged sothat their absorption axes are deviated from a parallel Nicols state,the second stacked polarizers are arranged so that their absorption axesare deviated from a parallel Nicols state, the first layer including thefirst stacked polarizers has a first polarizer and a second polarizerwhich are sequentially stacked from the first light-transmittingsubstrate side, and the first stacked polarizers and the second stackedpolarizers are arranged so that their absorption axes are in a crossedNicols state.

With respect to a display device of the invention, in the case wherelight from a light source called a backlight is transmitted through alayer including stacked polarizers on a side opposite to a viewing sideto a display element and extracted from a layer including stackedpolarizers on a viewing side, it is preferable that the absorption axesof the polarizers on the side (backlight side) opposite to the viewingside are in a parallel Nicols state, thereby transmittance of the lightfrom the backlight is increased.

Further, a layer including stacked polarizers of the display device ofthe invention may have a structure in which a stack of a plurality ofpolarizers is provided between a pair of protective layers or astructure in which each polarizer is sandwiched between a pair ofprotective layers. Further, a structure may be used in which ananti-reflective film, an antiglare film, or the like is provided on theviewing side of the layer including stacked polarizers.

With a simple structure in which a plurality of polarizers havingdifferent wavelength distributions of extinction coefficients arestacked and provided so that their absorption axes are deviated fromeach other, light leakage can be reduced, and contrast ratio of adisplay device can be increased. Further, such a high performancedisplay device can be manufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 2A and 2B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 3A to 3C are a cross-sectional view, a perspective view, and aschematic diagram of a display device of the present invention;

FIGS. 4A and 4B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIG. 5 illustrates a display device of the present invention;

FIGS. 6A and 6B each illustrate a display device of the presentinvention;

FIGS. 7A and 7B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 8A and 8B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 9A to 9C are a cross-sectional view, a perspective view, and aschematic diagram of a display device of the present invention;

FIGS. 10A to 10C are a cross-sectional view, a perspective view, and aschematic diagram of a display device of the present invention;

FIGS. 11A and 11B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 12A and 12B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 13A to 13C are cross-sectional views each illustrating a structureof a layer including a polarizer of the present invention;

FIGS. 14A and 14B are a top view and a cross-sectional view of a displaydevice of the present invention;

FIG. 15 is a cross-sectional view of a display device of the presentinvention;

FIGS. 16A to 16C are top views each showing a display device of thepresent invention;

FIGS. 17A and 17B are top views each showing a display device of thepresent invention;

FIGS. 18A and 18B are cross-sectional views each showing a displaydevice of the present invention;

FIGS. 19A to 19D are cross-sectional views showing an irradiation meansof a display device of the present invention;

FIG. 20 is a block diagram illustrating a basic structure of anelectronic device to which the present invention is applied;

FIGS. 21A to 21C illustrate electronic devices of the present invention;

FIGS. 22A to 22E illustrate electronic devices of the present invention;

FIG. 23 is a cross-sectional view of a display device of the presentinvention;

FIGS. 24A to 24C are block diagrams illustrating a display device of thepresent invention;

FIGS. 25A to 25D are top views each illustrating a display device of thepresent invention;

FIG. 26A to 26D are top views each illustrating a display device of thepresent invention;

FIGS. 27A1 to 27C2 are cross-sectional views illustrating a liquidcrystal mode of the present invention;

FIGS. 28A1 to 28B2 are cross-sectional views illustrating a liquidcrystal mode of the present invention;

FIGS. 29A1 to 29B2 are cross-sectional views illustrating a liquidcrystal mode of the present invention;

FIGS. 30A and 30B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIGS. 31A and 31B are a cross-sectional view and a perspective viewrespectively of a display device of the present invention;

FIG. 32 is a diagram showing experimental conditions of Embodiment 1;

FIG. 33 is a graph showing an experimental result of Embodiment 1;

FIGS. 34A to 34C are diagrams showing experimental conditions ofEmbodiment 1;

FIG. 35 is a graph showing an experimental result of Embodiment 1;

FIG. 36 is a graph showing an experimental result of Embodiment 1; and

FIG. 37 is a graph showing an experimental result of Embodiment 1.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Modes

Hereinafter, embodiment modes and an embodiment of the present inventionwill be explained with reference to the drawings. Note that it is easilyunderstood by those skilled in the art that forms and details of theinvention can be variously changed without departing from the spirit andscope of the invention. Therefore, the present invention should not beconstrued as being limited to the content of the embodiment modes. Notethat common portions and portions having similar functions are denotedby the same reference numerals in all diagrams for describing embodimentmodes, and description thereof will not be repeated.

Embodiment Mode 1

In this embodiment mode, a concept of a display device in which a pairof stacked layers each including a polarizer using the present inventionis provided will be explained.

FIG. 1A is a cross-sectional view of a display device having a pair ofstacked layers each including a polarizer, in which the wave lengthdistributions of the extinction coefficients with respect to theabsorption axes are different, and a structure in which at least one ofthe layers having the polarizers is disposed so as to be deviated from aparallel Nicols state. FIG. 1B is a perspective view of the displaydevice. In this embodiment mode, an example of a liquid crystal displaydevice having a liquid crystal element as a display element will bedescribed.

As shown in FIG. 1A, a layer 100 having a liquid crystal element issandwiched between a first substrate 101 and a second substrate 102which are arranged so as to face each other.

In this embodiment mode, stacked layers each including a polarizer areprovided on an outer side of a substrate, where the substrate is not incontact with a layer having a liquid crystal element. Specifically, asshown in FIG. 1A, a first layer 103 including a polarizer and a secondlayer 104 including a polarizer are provided on a first substrate 101side. Meanwhile, a third layer 105 including a polarizer and a fourthlayer 106 including a polarizer are provided on a second substrate 102side. In this embodiment mode, in a pair of layers each including apolarizer, in which the wavelength distributions of the extinctioncoefficients with respect to the absorption axes are different, at leastone of the stacked layers each including a polarizers is deviated from aparallel Nicols state. Specifically, as shown in FIG. 1B, the firstlayer 103 including a polarizer and the second layer 104 including apolarizer are stacked so that the absorption axis (A) of the first layer103 and the absorption axis (B) of the second layer 104 where thewavelength distributions of the extinction coefficients are differentare deviated from a parallel state. Further, the third layer 105including a polarizer and the fourth layer 106 including a polarizer arestacked so that the absorption axis (C) of the third layer 105 and theabsorption axis (D) of the fourth layer 106 where the wavelengthdistributions of the extinction coefficients are different are inparallel, that is, in a parallel Nicols state.

A polarizer has inconstant dependence of the absorption properties on awavelength, and the absorption properties with respect to a certainwavelength region are lower than that with respective to anotherwavelength region, that is, the polarizer has properties of hardlyabsorbing light of the certain wavelength region. Accordingly, even whena plurality of polarizers of the same type is used in attempting toimprove contrast ratio, a certain wavelength region of light which ishardly absorbed remains. In accordance with the present invention, thewavelength region of light which is hardly absorbed can be eliminated orreduced by combining and stacking polarizers where the wavelengthdistributions of the extinction coefficients with respect to theabsorption axis are different. Therefore, even slight light leakage canbe prevented, and contrast ratio can be further improved.

Each of the substrates is a light-transmitting insulating substrate(hereinafter also referred to as a light-transmitting substrate). Thesubstrate is especially transparent to light in the visible wavelengthrange. As the substrates, for example, a glass substrate made of bariumborosilicate glass, aluminoborosilicate glass, or the like; a quartzsubstrate; or the like can be used. Alternatively, a substrate formed ofplastic typified by polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), and polyether sulfone (PES), or a flexible syntheticresin such as acrylic can be used as the substrates. Further, a film(formed of polypropylene, polyester, vinyl, polyvinyl fluoride,polyvinyl chloride, or the like), a base film (formed of polyester orpolyamide, an inorganic deposition film, or the like) may be used as thesubstrates.

Further, although not shown in FIGS. 1A and 1B, an irradiation meanssuch as a backlight is disposed below the fourth layer 106 including thepolarizer.

In this embodiment mode, the first layer 103 including the polarizer andthe third layer 105 including the polarizer are arranged so as to be ina crossed Nicols state. The first layer 103 including the polarizer andthe third layer 105 including the polarizer may be deviated from thecrossed Nicols state within the range where predetermined black displayis obtained.

FIG. 5 is a top view of angles between the absorption axis (A) of thefirst layer 103 including the polarizer, the absorption axis (B) of thesecond layer 104 including the polarizer, the absorption axis (C) of thethird layer 105 including the polarizer, and the absorption axis (D) ofthe fourth layer 106 including the polarizer. The first layer 103including the polarizer and the second layer 104 including the polarizerare stacked in such a way that the absorption axis (A) and theabsorption axis (B) are deviated by an angle θ. In this embodiment mode,the third layer 105 including the polarizer and the fourth layer 106including the polarizer are arranged in such a way that the absorptionaxis (C) and the absorption axis (D) are in a parallel Nicols state.

Note that a polarizer characteristically has a transmission axisperpendicular to the absorption axis. Therefore, a state where thetransmission axes are parallel to each other can also be referred to asa parallel Nicols state, and a state where transmission axes areperpendicular to each other can also be referred to as a crossed Nicolsstate.

Note that the number of the stacked layers each including a polarizer ahaving different wavelength distribution of extinction coefficient fromeach other in FIGS. 1A and 1B is two; however, the present invention isnot limited thereto and a multilayer structure having more than twolayers may be used. An example of further stacking a fifth layer 121including a polarizer over the first layer 103 including a polarizer andthe second layer 104 including the polarizer which have differentwavelength distributions of extinction coefficients is shown in FIGS. 7Aand 7B. In FIGS. 7A and 7B, the fifth layer 121 including the polarizerhas an absorption axis (G), and the absorption axis (G) is parallel tothe absorption axis (B) of the second layer 104 including the polarizer,and deviated from the absorption axis (A) of the first layer 103including the polarizer. In other words, as shown in FIG. 6A, the fifthlayer 121 including the polarizer and the second layer 104 including thepolarizer are stacked so that their absorption axes are in a parallelNicols state.

Further, the wavelength distribution of the extinction coefficient withrespect to the absorption axis of the fifth layer 121 including thepolarizer may be equal to or different from that with respect to thefirst layer 103 including the polarizer or the second layer 104including the polarizer which is to be stacked together therewith. Inthis embodiment mode, the wavelength distribution of the extinctioncoefficient with respect to the absorption axis of the fifth layer 121including the polarizer is different from that with respect to those ofthe first layer 103 including the polarizer and the second layer 104including the polarizer. Thus, when the wavelength distributions of theextinction coefficients with respect to the absorption axes of thepolarizers in the stacked layers are different, the wavelength range oflight which can be absorbed can be extended; thus, even slight lightleakage can be prevented. In the present invention, a stack in whichabsorption axes of the polarizers are deviated from a parallel Nicolsstate may be used in a plurality of stacked layers each including apolarizer. Similarly, at least two polarizers having differentwavelength distributions of extinction coefficients may be used in aplurality of stacked layers each including a polarizer.

Further, a fifth layer including a polarizer may be provided between thefirst layer 103 including the polarizer and the second layer 104including the polarizer in such a manner the fifth layer and the firstlayer 103 are in a parallel Nicols state. FIGS. 8A and 8B show anexample in which a fifth layer 122 including a polarizer is stackedbetween the first layer 103 including the polarizer and the second layer104 including the polarizer. In FIG. 8, the fifth layer 122 includingthe polarizer has an absorption axis (H), and the absorption axis (H) isparallel to the absorption axis (A) of the first layer 103 including thepolarizer, and deviated from the absorption axis (B) of the second layer104 including the polarizer. Accordingly, as shown in FIG. 6B, the fifthlayer 122 including the polarizer, the first layer 103 including thepolarizer, and the second layer 104 including the polarizer are stackedso that the absorption axes of the fifth layer 122 and the first layer103 are in a parallel Nicols state, and the absorption axes of the fifthlayer 122 and the second layer 104 are deviated by a deviated angle θ.

Further, the stack including the third layer 105 including the polarizerand the fourth layer 106 including the polarizer which are stacked in aparallel Nicols state on a light source side may be replaced by onelayer (See FIG. 31). In that case, a stack including the first layer 103including the polarizer and the second layer 104 including the polarizerhaving a different wavelength distribution of extinction coefficientfrom each other is disposed on the viewing side, and the third layer 105including the polarizer is disposed on the light source side with alayer including a liquid crystal element therebetween. The structure asshown in FIG. 31 may preferably be used when the amount of light fromthe light source is desired not to decrease.

As in this embodiment mode, a pair of stacked layers includingpolarizers can be applied to a display device where light can beextracted from both sides of a substrate.

Thus, in a pair of stacked layers each including polarizers, polarizersin at least one of the layers each including polarizers having differentwavelength distributions of extinction coefficients, preferably, thelayer on a viewing side, are provided so that the absorption axes of thepolarizers are deviated from a parallel Nicols state, thereby reducinglight leakage in the directions of the absorption axes. Thus, contrastratio of the display device can be increased.

Embodiment Mode 2

This embodiment mode will describe a concept of a display deviceprovided with a retardation plate in addition to a pair of stackedlayers each including a polarizing plate having a different wavelengthdistribution of extinction coefficient from each other with respect tothe absorption axes unlike the above embodiment mode.

FIG. 2A is a cross-sectional view of a display device in which one ofthe pair of stacked layers each including a polarizer having a differentwavelength distribution of extinction coefficient from each other withrespect to the absorption axis is stacked to be deviated from a parallelNicols state, and retardation plates are provided between the pair ofstacked layers each including a polarizer and substrates respectively,while FIG. 2B is a perspective view of the display device. In thisembodiment mode, a liquid crystal display device having a liquid crystalelement as a display element will be explained as an example.

As shown in FIG. 2A, a layer 100 including a liquid crystal element issandwiched between a first substrate 101 and a second substrate 102which are disposed to face each other.

As shown in FIG. 2A, a first layer 103 including a polarizer and asecond layer 104 including a polarizer are provided on a first substrate101 side. A third layer 105 including a polarizer and a fourth layer 106including a polarizer are provided on a second substrate 102 side.

As shown in FIG. 2B, the first layer 103 including the polarizer and thesecond layer 104 including the polarizer are arranged so that theabsorption axes of the polarizing plate having different wavelengthdistributions of extinction coefficients are deviated from a parallelNicols state. Further, a retardation plate 113 is provided between thestacked layers each including the polarizing plate having a differentwavelength distribution of extinction coefficient from each other withrespect to the absorption axes and the first substrate 101.

Further, as shown in FIG. 2B, the third layer 105 including thepolarizer and the fourth layer 106 including the polarizer are providedon the second substrate 102 side. The third layer 105 including thepolarizer and the fourth layer 106 including the polarizer are arrangedto be in a parallel Nicols state. In addition, a retardation plate 114is provided between the stacked layers each including the polarizer andthe second substrate 102.

In addition, although not shown in FIGS. 2A and 2B, an irradiation meanssuch as a backlight is disposed below the fourth layer 106 including thepolarizer.

The retardation plate may be, for example, a film in which liquidcrystals are hybrid-aligned, a film in which liquid crystals aretwist-aligned, a uniaxial retardation plate, or a biaxial retardationplate. Using such retardation plates, the viewing angle of the displaydevice can be extended. The film in which liquid crystals arehybrid-aligned is a compound film in which a triacetyl cellulose (TAC)film is used as a base and discotic liquid crystals having negativeuniaxiality are hybrid-aligned to obtain optical anisotropy.

The uniaxial retardation plate is formed by stretching a resin in onedirection. Meanwhile, a biaxial retardation plate is formed bystretching a resin into an axis in a crosswise direction, and thengently stretching the resin into an axis in a lengthwise direction. Theresin used here may be cyclo-olefin polymer (COP), polycarbonate (PC),polymethyl methacrylate (PMMA), polystyrene (PS), polyether sulfone(PES), polyphenylene sulfide (PPS), polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polypropylene (PP), polyphenylene oxide(PPO), polyarylate (PAR), polyimide (PI), polytetrafluoroethylene(PTFE), or the like.

The film in which liquid crystals are hybrid-aligned is a film formed byusing a triacetyl cellulose (TAC) film as a base and hybrid-aligningdiscotic liquid crystals or nematic liquid crystal molecules. Theretardation plate can be attached to a light-transmitting substrateafter being attached to a layer including a polarizer.

Circular polarization, elliptical polarization, or the like can beperformed by combining a retardation plate and stacked polarizers.Further, a plurality of retardation plates may be used instead of onepolarizer. Note that a retardation plate characteristically has a fastaxis perpendicular to a slow axis. Therefore, the arrangement can bedetermined based on fast axes instead of slow axes.

Note that in this embodiment mode, the first layer 103 including thepolarizer and the third layer 105 including the polarizer are arrangedto be in a crossed Nicols state. The first layer 103 including thepolarizer and the third layer 105 including the polarizer may bedeviated as long as display of a predetermined black level can beobtained.

Note that the number of the stacked layers each including a polarizerhaving a different wavelength distribution of extinction coefficientfrom each other in FIGS. 2A and 2B is two; however, the presentinvention is not limited thereto and a multilayer structure having morethan two layers may be used. A fifth layer including a polarizer may beprovided between the first layer 103 including the polarizer and thesecond layer 104 including the polarizer in such a manner the fifthlayer and the first layer 103 are in a parallel Nicols state. An exampleof further stacking a fifth layer 122 including a polarizer over thefirst layer 103 including a polarizer and the second layer 104 includingthe polarizer is shown in FIGS. 11A and 11B. In FIGS. 11A and 11B, thefifth layer 122 including the polarizer has an absorption axis (H), andthe absorption axis (H) is parallel to the absorption axis (A) of thefirst layer 103 including the polarizer, and deviated from theabsorption axis (B) of the second layer 104 including the polarizer.Accordingly, the fifth layer 122 including the polarizer, the firstlayer 103 including the polarizer, and the second layer 104 includingthe polarizer are stacked so that the absorption axes of the fifth layer122 and the first layer 103 are in a parallel Nicols state, and theabsorption axes of the fifth layer 122 and the second layer 104 aredeviated by a deviated angle θ.

Further, the wavelength distribution of the extinction coefficient withrespect to the absorption axis of the fifth layer 122 including thepolarizer may be equal to or different from that with respect to thefirst layer 103 including the polarizer or the second layer 104including the polarizer which is to be stacked together therewith. Inthis embodiment mode, the wavelength distribution of the extinctioncoefficient with respect to the absorption axis of the fifth layer 122including the polarizer is different from that with respect to those ofthe first layer 103 including the polarizer and the second layer 104including the polarizer. Thus, when the wavelength distributions of theextinction coefficients with respect to the absorption axes of thepolarizers in the stacked layers are different, the wavelength range oflight which can be absorbed can be extended; thus, even slight lightleakage can be prevented.

As in this embodiment mode, a pair of stacked layers each includingpolarizers can be applied to a display device where light can beextracted from both sides of a substrate.

Thus, in a structure having a pair of stacked layers each includingpolarizers and a retardation plate, polarizers in at least one of thelayers each including polarizers having different wavelengthdistributions of extinction coefficients, preferably, the layer on aviewing side, are provided so that their absorption axes are deviatedfrom a parallel Nicols state, thereby reducing light leakage in thedirections of the absorption axes. Thus, contrast ratio of the displaydevice can be increased.

Embodiment Mode 3

This embodiment mode will describe a concept of a display deviceprovided with stacked layers each including a polarizing plate having adifferent wavelength distribution of extinction coefficient from eachother with respect to the absorption axes unlike the above embodimentmode. The like parts or parts having like functions are denoted by thesame reference numerals, and the description of them will not berepeated.

FIG. 3A is a cross-sectional view of a display device having stackedlayers including polarizers, which are arranged to be deviated from aparallel Nicols state, and FIG. 3B shows a perspective view of thedisplay device. In this embodiment mode, an example of a liquid crystaldisplay device including a liquid crystal element as a display elementwill be described.

As shown in FIG. 3A, a layer 100 including a liquid crystal element issandwiched between a first substrate 101 and a second substrate 102which are disposed to face each other.

Stacked layers each including a polarizer are provided on an outer sideof a substrate, where the substrate is not in contact with a layerhaving a liquid crystal element. A first layer 103 including a polarizerand a second layer 104 including a polarizer are provided on a firstsubstrate 101 side. Here, the first layer 103 including the polarizerand the second layer 104 including the polarizer are arranged so thattheir absorption axes are deviated to be in a parallel Nicols state. Inthis embodiment mode, the wavelength distributions of the extinctioncoefficients of the polarizers in the first layer 103 and the secondlayer 104 with respect to the absorption axes are different from eachother.

In this embodiment mode, a reflector plate may be provided in addition.The reflector plate can be provided by forming a pixel electrode from ahighly reflective material on an outer side of the second substrate 102.

As shown in FIG. 3B, the first layer 103 including the polarizer havingan absorption axis (A) and the second layer 104 including a polarizerhaving an absorption axis (B) are stacked so that their absorption axesare deviated from each other. Thus, when layers including polarizers arestacked so that their absorption axes are deviated, contrast ratio canbe increased.

Further, even when a plurality of polarizers of the same type is used inattempting to improve contrast ratio, a certain wavelength region oflight which is hardly absorbed remains. In accordance with the presentinvention, the wavelength region of light which is hardly absorbed canbe eliminated or reduced by combining and stacking polarizers where thewavelength distributions of the extinction coefficients with respect tothe absorption axis are different. Therefore, even slight light leakagecan be prevented, and contrast ratio can be further improved.

FIG. 3C illustrates an angle formed between the absorption axis (A) ofthe polarizer included in the first layer 103 and the absorption axis(B) of the polarizer included in the second layer 104, which is viewedfrom above. The first layer 103 including the polarizer and the secondlayer 104 including the polarizer are stacked in such a way that theabsorption axis (A) and the absorption axis (B) are deviated by an angleof θ.

Note that the number of the stacked layers each including a polarizerhaving a different wavelength distribution of extinction coefficientfrom each other in FIGS. 3A to 3C is two; however, the present inventionis not limited thereto and a multilayer structure having more than twolayers may be used. An example of further stacking a fifth layer 121including a polarizer over the first layer 103 including a polarizer andthe second layer 104 including the polarizer is shown in FIGS. 11A to11C. In FIGS. 11A and 11B, the fifth layer 121 including the polarizerhas an absorption axis (G), and the absorption axis (G) is parallel tothe absorption axis (B) of the second layer 104 including the polarizer,and deviated from the absorption axis (A) of the first layer 103including the polarizer. In other words, as shown in FIG. 9C, the fifthlayer 121 including the polarizer and the second layer 104 including thepolarizer are stacked so that their absorption axes are in a parallelNicols state.

Further, a fifth layer including a polarizer may be provided between thefirst layer 103 including the polarizer and the second layer 104including the polarizer in such a manner the fifth layer and the firstlayer 103 are in a parallel Nicols state. FIGS. 10A to 10C show anexample in which a fifth layer 122 including a polarizer is stackedbetween the first layer 103 including the polarizer and the second layer104 including the polarizer. In FIGS. 10A and 10B, the fifth layer 122including the polarizer has an absorption axis (H), and the absorptionaxis (H) is parallel to the absorption axis (A) of the first layer 103including the polarizer, and deviated from the absorption axis (B) ofthe second layer 104 including the polarizer. Accordingly, as shown inFIG. 10C, the fifth layer 122 including the polarizer, the first layer103 including the polarizer, and the second layer 104 including thepolarizer are stacked so that the absorption axes of the fifth layer 122and the first layer 103 are in a parallel Nicols state, and theabsorption axes of the fifth layer 122 and the second layer 104 aredeviated by a deviated angle θ.

Further, the wavelength distribution of the extinction coefficient withrespect to the absorption axis of the fifth layer 122 including thepolarizer may be equal to or different from that with respect to thefirst layer 103 including the polarizer or the second layer 104including the polarizer which is to be stacked together therewith. Inthis embodiment mode, the wavelength distribution of the extinctioncoefficient with respect to the absorption axis of the fifth layer 122including the polarizer is different from that with respect to those ofthe first layer 103 including the polarizer and the second layer 104including the polarizer. Thus, when the wavelength distributions of theextinction coefficients with respect to the absorption axes of thepolarizers in the stacked layers are different, the wavelength range oflight which can be absorbed can be extended; thus, even slight lightleakage can be prevented.

As in this embodiment mode, the structure in which layers includingpolarizers are stacked over one side of a substrate can be applied to adisplay device where light can be extracted from one sides of asubstrate.

Thus, the layers each including a polarizer having a differentwavelength distribution of extinction coefficient from each other areprovided so that their absorption axes are deviated from a parallelNicols state, thereby reducing light leakage in the directions of theabsorption axes. Thus, contrast ratio of the display device can beincreased.

Embodiment Mode 4

This embodiment mode will describe a concept of a display deviceprovided with a retardation plate in addition to layers each including apolarizing plate having a different wavelength distribution ofextinction coefficient from each other with respect to the absorptionaxes, which are stacked on a viewing side unlike the above embodimentmode. The like parts or parts having like functions are denoted by thesame reference numerals, and the description of them will not berepeated.

FIG. 4A is a cross-sectional view of a display device in which aretardation plate is provided between a substrate and layers including apolarizers which are stacked to be deviated from a parallel Nicolsstate, and FIG. 4B is a perspective view of the display device. In thisembodiment mode, an example of a liquid crystal display device includinga liquid crystal element as a display element will be described.

As shown in FIG. 3A, a layer 100 including a liquid crystal element issandwiched between a first substrate 101 and a second substrate 102which are disposed to face each other.

As shown in FIG. 4B, the first layer 103 including the polarizer and thesecond layer 104 including the polarizer are provided on the firstsubstrate 101 side. Here, the first layer 103 including the polarizerand the second layer 104 including the polarizer are arranged to bedeviated from a parallel Nicols state. In addition, a retardation plate113 is provided between the first substrate 101 and the stacked layerseach including the polarizer. In this embodiment mode, the wavelengthdistributions of the extinction coefficients of the polarizers in thefirst layer 103 and the second layer 104 with respect to the absorptionaxes are different from each other.

In this embodiment mode, a reflector plate may be provided in addition.The reflector plate can be provided by forming a pixel electrode from ahighly reflective material on an outer side of the second substrate 102.

As shown in FIG. 4B, the first layer 103 including the polarizer havingan absorption axis (A) and the second layer 104 including a polarizerhaving an absorption axis (B) are stacked so that their absorption axesare deviated from each other. Further, the absorption axis (A) of thepolarizer included in the first layer 103 may preferably be arranged tobe deviated from the slow axis of the retardation plate 113 by 45°.Thus, when layers including polarizers are stacked so that theirabsorption axes are deviated and a retardation plate is provided,contrast ratio can be increased.

Note that the number of the stacked layers each including a polarizerhaving a different wavelength distribution of extinction coefficientfrom each other in FIGS. 4A and 4B is two; however, the presentinvention is not limited thereto and a multilayer structure having morethan two layers may be used. An example of further stacking a fifthlayer 122 including a polarizer over the first layer 103 including apolarizer and the second layer 104 including the polarizer is shown inFIGS. 12A to 12C. In FIGS. 12A and 12B, the fifth layer 122 includingthe polarizer has an absorption axis (G), and the absorption axis (G) isparallel to the absorption axis (B) of the second layer 104 includingthe polarizer, and deviated from the absorption axis (A) of the firstlayer 103 including the polarizer. In other words, the fifth layer 122including the polarizer and the second layer 104 including the polarizerare stacked so that their absorption axes are in a parallel Nicolsstate.

Further, the wavelength distribution of the extinction coefficient withrespect to the absorption axis of the fifth layer 122 including thepolarizer may be equal to or different from that with respect to thefirst layer 103 including the polarizer or the second layer 104including the polarizer which is to be stacked together therewith. Inthis embodiment mode, the wavelength distribution of the extinctioncoefficient with respect to the absorption axis of the fifth layer 122including the polarizer is different from that with respect to those ofthe first layer 103 including the polarizer and the second layer 104including the polarizer. Thus, when the wavelength distributions of theextinction coefficients with respect to the absorption axes of thepolarizers in the stacked layers are different, the wavelength range oflight which can be absorbed can be extended; thus, even slight lightleakage can be prevented.

As in this embodiment mode, the structure in which layers includingpolarizers are stacked over one side of a substrate can be applied to adisplay device where light can be extracted from one sides of asubstrate.

Thus, the layers each including a polarizer having a differentwavelength distribution of extinction coefficient from each other areprovided so that their absorption axes are deviated from a parallelNicols state and a retardation plate is provided in addition, therebyreducing light leakage in the directions of the absorption axes. Thus,contrast ratio of the display device can be increased.

Embodiment Mode 5

In this embodiment mode, structures of polarizers having differentwavelength distributions of extinction coefficients with respect to theabsorption axes are different from each other which can be used for thepresent invention will be described with reference to FIGS. 13A to 13C.

In the present invention, a layer including a polarizer includes atleast a polarizer having a specific absorption axis. A single layerpolarizer, or a polarizer inserted between protective layers may beused. FIGS. 13A to 13C illustrate examples of layered structures oflayers including polarizers in accordance with the present invention. InFIG. 13A, a layer including a polarizer having a protective layer 50 a,a first polarizer 51, and a protective layer 50 b is stacked togetherwith a layer including a polarizer having a protective layer 50 c, asecond polarizer 52, and a protective layer 50 d and the stackconstitutes a layer including stacked polarizers. Thus, in the presentinvention, “stacked polarizers” includes a stack including polarizers inwhich a protective layer is interposed therebetween, where thepolarizers are not stacked in contact with each other. Accordingly “alayer including stacked polarizers” may mean the whole stack includingthe layer including the polarizer having the protective layer 50 a, thefirst polarizer 51, and the protective layer 50 b and a layer includingthe polarizer having the protective layer 50 c, the second polarizer 52,and the protective layer 50 d. Further, in this specification, the layerincluding a polarizer having the protective layer 50 a, the firstpolarizer 51, and the protective layer 50 b is also referred to as apolarizing plate. Therefore, what is shown in FIG. 13A can also bereferred to as a stack including polarizing plates. In FIG. 13A, thefirst polarizer 51 and the second polarizer 52 are stacked so that theirabsorption axes are deviated from each other. Further, wavelengthdistributions of extinction coefficients with respect to the absorptionaxes of the first polarizer 51 and the second polarizer 52 are differentfrom each other.

FIG. 13B shows a layer including stacked polarizers, which is a stackhaving a protective layer 56 a, a first polarizer 57, a second polarizer58, and a protective layer 56 b. The structure shown in FIG. 13B can beexpressed as “a stack of the protective layer 56 a and the protectivelayer 56 b is provided so that the stacked polarizers including thefirst polarizer 57 and the second polarizer 58 are providedtherebetween”, or as “a layer including a polarizer having theprotective layer 56 a and the polarizer 57 is stacked together with alayer including a polarizer having the polarizer 58 and the protectivelayer 56 b”. FIG. 13B shows an example in which polarizers are directlystacked without protective layers therebetween unlike in FIG. 13A. Thisstructure has an advantage in that the layer including stackedpolarizers which is a polarizing means can be made thinner, and thenumber of stacked protective layers may be small; thus, the process canbe simplified at low cost. In FIG. 13B, the first polarizer 57 and thesecond polarizer 58 are stacked so that their absorption axes aredeviated from each other. Further, the wavelength distributions of theextinction coefficients with respect to the absorption axes of the firstpolarizer 57 and the second polarizer 58 are different from each other.

FIG. 13C shows a structure in which polarizers are stacked together withone protective layer therebetween, which is in between the structuresshown in FIG. 13A and FIG. 13B. FIG. 13C shows a layer including stackedpolarizers, which is a stack including a protective layer 60 a, a firstpolarizer 61, a protective layer 60 b, a second polarizer 62, and aprotective layer 60 c. Such a structure in which protective layers andpolarizers are stacked alternately may be used. A polarizer in thepresent invention is in a film form, and can be referred to as apolarizing film or a polarizing layer. In FIG. 13C, the first polarizer61 and the second polarizer 62 are stacked so that their absorption axesare deviated from each other. In addition, wavelength distributions ofextinction coefficients with respect to the absorption axes of the firstpolarizer 61 and the second polarizer 62 are different from each other.

FIGS. 13A to 13C show examples of stacking two layers of polarizers;however, three layers of polarizers may be stacked, or a greater numberof layers of polarizers may be provided. The manner of providingprotective layers is also not limited to the structures shown in FIG.13A to 13C. Further, a structure may be used in which the layerincluding the stacked polarizers in FIG. 13A is stacked together withthe layer including the stacked polarizers in FIG. 13B. In the case ofpolarizers which easily deteriorate due to moisture or temperaturechange depending on the material of the polarizer, the polarizers can beprotected by covering the polarizers as shown in FIG. 13A; thus,reliability can be improved. As shown in FIG. 1, in the case ofproviding polarizers so as to interpose a layer including a displayelement therebetween, the layered structure of the polarizers on aviewing side ma be the same as or different from the layered structureof the polarizers on the opposite side opposite with the display elementin-between. Thus, the layered structure of the stacked polarizers may beset as appropriate depending on the properties of the polarizers andfunctions required for the display device. For example, in EmbodimentMode 1, each of the layers including the polarizers 103 and 104, and thelayer including the polarizers 105 and 106 constitutes a layer includingstacked polarizers; however, the layers may have any of the structuresshown in FIGS. 13A to 13C, or one of the layers may have the structurein FIG. 13A and the other has the structure shown in FIG. 13B.

Further, the layers including stacked polarizers may have a structure inwhich bonding layers (adhesive layers) are provided between protectivelayers, between polarizers, and between the protective layer and thepolarizer to bond them. In this case, the adhesion layers are requiredto have light-transmitting properties as the protective layers have. Aretardation plate may be stacked together with a polarizer. Theretardation plate also may have a structure in which a retardation filmis provided between a pair of protective layers and may be stackedtogether with a polarizer with one or a plurality of protective layersin-between, or may be directly stacked together with the polarizer sothat a protective layer, a retardation film, a polarizer, and aprotective layer are sequentially stacked together. For example, in FIG.13B, when the protective layer 56 a is on a light-transmitting substrateside, a retardation film may be provided between the protective layer 56a and the polarizer 57, and another retardation film is provided betweenthe light-transmitting substrate and the polarizer. Further, a moredurable protective film or the like may be provided for example as asurface protective layer on the protective layer 50 d. Further, ananti-reflective film which prevents reflection of external light on ascreen surface or an antiglare film which prevents glare or dazzle on ascreen may be provided. Further, when a layer including a polarizer(polarizing plate) is bonded to a substrate, an adhesion layer of anacrylic adhesive or the like may be used.

The polarizer transmits only light vibrating in a certain direction andabsorbs other light. A uniaxially stretched resin film to whichdichromatic pigment is adsorbed and oriented can be used. As the resin,PVA (polyvinyl alcohol) can be used. PVA has high transparency andintensity, and can be easily attached to TAC (triacetyl cellulose) thatis used as a protective layer (also referred to as a protective filmbecause of its shape). As the pigment, iodine-based pigment anddye-based pigment can be used. For example, in a case of iodine-basedpigment, iodine having high dichroism is adsorbed as a high ion to a PVAresin film and stretched in a boric acid aqueous solution, whereby theiodine is arranged as a chain polymer, and a polarizer shows a highpolarizing characteristic. On the other hand, dye-based pigment in whichdye having high dichroism is used instead of iodine has superiority inheat resistance and durability.

The protective layer reinforces intensity of the polarizer and preventsdeterioration due to the temperature and moisture. As the protectivelayer, a film such as a TAC (triacetyl cellulose) film, a COP (cyclicolefin polymer-based) film, a PC (polycarbonate) film can be used. TAChas transparency, low birefringence, and superiority in an adhesiveproperty to PVA that is used for the polarizer. COP is a resin filmhaving superiority in heat resistance, moisture resistance, anddurability. Further, iodine-based pigment and dye-system pigment can bemixed to be used.

As for the layer including a polarizer, for example, an adhesivesurface, TAC (triacetyl cellulose) that is a protective layer, a mixedlayer of iodine and PVA (polyvinyl alcohol) that is a polarizer, and TACthat is a protective layer are sequentially stacked from a substrateside. The polarization degree can be controlled by the mixed layer ofiodine and PVA (polyvinyl alcohol). Alternatively, an inorganic materialmay be used for a polarizer. The layer including a polarizer may bereferred to as a polarizing plate because of its shape.

This embodiment mode can be used in combination with any one of theabove embodiment modes.

Thus, polarizers having different wavelength distributions of extinctioncoefficients from each other are stacked so that their absorption axesare deviated from a parallel Nicols state, thereby reducing lightleakage in the directions of the absorption axes. Thus, contrast ratioof the display device can be increased.

Embodiment Mode 6

In this embodiment mode, a structure of a liquid crystal display devicehaving a pair of stacked layers each including a polarizer havingdifferent wavelength distribution of extinction coefficient with respectto the absorption axes with each other will be explained, in whichpolarizers of at least one of the pars of the stacked layers eachincluding a polarizer are arranged so that the transmission axes aredeviated from each other.

FIG. 16A is a top view showing a structure of a display panel inaccordance with the present invention, where a pixel portion 2701 inwhich pixels 2702 are arranged in matrix, a scanning line input terminal2703, and a signal line input terminal 2704 are formed over a substrate2700 having an insulating surface. The number of pixels may be providedaccording to various standards: the number of pixels of XGA for RGBfull-color display may be 1024×768×3 (RGB), that of UXGA for RGBfull-color display may be 1600×1200×3 (RGB), and that corresponding to afull-speck high vision for RGB full-color display may be 1920×1080×3(RGB).

The pixels 2702 are arranged in matrix by intersecting scanning linesextended from the scanning line input terminal 2703 with signal linesextended from the signal line input terminal 2704. Each pixel 2702 isprovided with a switching element and a pixel electrode layer connectedto the switching element. A typical example of the switching element isa TFT. A gate electrode layer side of the TFT is connected to thescanning line, and a source or drain side thereof is connected to thesignal line, thereby each pixel can be controlled independently by asignal inputted from the external.

FIG. 16A shows a structure of the display panel in which signalsinputted to a scanning line and a signal line are controlled by anexternal driver circuit. Alternatively, driver ICs 2751 may be mountedon the substrate 2700 by COG (Chip on Glass) as shown in FIG. 17A.Further, the driver ICs may also be mounted by TAB (Tape AutomatedBonding) as shown in FIG. 17B. The driver ICs may be one formed over asingle crystalline semiconductor substrate or may be a circuit that isformed using a TFT over a glass substrate. In FIGS. 17A and 17B, eachdriver IC 2751 is connected to an FPC (Flexible printed circuit) 2750.

Further, in the case where a TFT provided in a pixel is formed using asemiconductor having crystallinity, a scanning line driver circuit 3702can also be formed over a substrate 3700 as shown in FIG. 16B. In FIG.16B, a pixel portion 3701 connected to a signal line input terminal 3704is controlled by an external driver circuit similarly to that in FIG.16A. In a case where a TFT provided in a pixel is formed using apolycrystalline (microcrystalline) semiconductor, a single crystallinesemiconductor, or the like with high mobility, a pixel portion 4701, ascanning line driver circuit 4702, and a signal line driver circuit 4704can be formed over a substrate 4700 in an integrated manner in FIG. 16C.

FIG. 14A is a top view of a liquid crystal display device that has astacked layer including a polarizer, and FIG. 14B is a cross-sectionalview taken along a line C-D of FIG. 14A.

As shown in FIG. 14A, a pixel portion 606, a driver circuit area 608 awhich is a scan line driver circuit, and a driver circuit area 608 bwhich is a scan line driver circuit are sealed with a sealant 692between a substrate 600 and an opposite substrate 695. A driver circuitarea 607 which is a signal line driver circuit formed by an IC driver isprovided over the substrate 600. The pixel portion 606 is provided witha transistor 622 and a capacitor element 623, and the driver circuitarea 608 b is provided with a driver circuit including a transistor 620and a transistor 621. An insulating substrate similar to that of theabove embodiment mode can be applied to the substrate 600. It is aconcern that a substrate made from a synthetic resin generally has alower allowable heat resistance temperature compared to othersubstrates; however, it can be employed by being deviated after amanufacturing process using a substrate with higher heat resistance.

In the pixel portion 606, the transistor 622 that is to be a switchingelement through base insulating films 604 a and 604 b is provided. Inthis embodiment mode, a multi-gate thin film transistor (TFT) is usedfor the transistor 622, which includes a semiconductor layer having animpurity region serving as a source region and a drain region, a gateinsulating layer, a gate electrode layer having a stacked-layerstructure made of two layers, a source electrode layer, and a drainelectrode layer. The source electrode layer or the drain electrode layeris electrically connected so as to be in contact with the impurityregion of the semiconductor layer and a pixel electrode layer 630. Thethin film transistor can be manufactured by various methods. Forexample, a crystalline semiconductor film is applied as an active layer.A gate electrode is provided over the crystalline semiconductor filmthrough a gate insulating film. An impurity element can be added to theactive layer using the gate electrode. Addition of the impurity elementusing the gate electrode makes it unnecessary to form a mask foraddition of the impurity element. The gate electrode can have either asingle-layer structure or a stacked-layer structure. The impurity regioncan be made a high concentration impurity region or a low concentrationimpurity region by controlling the concentration thereof. A structure ofsuch a thin film transistor having such a low concentration impurityregion is referred to as an LDD (Lightly doped drain) structure. Inaddition, the low concentration impurity region can be formed to beoverlapped with the gate electrode. A structure of such a thin filmtransistor is referred to as a GOLD (Gate Overlapped LDD) structure.Polarity of the thin film transistor is to be an n-type by usingphosphorus (P) or the like in the impurity region. When polarity of thethin film transistor is to be a p-type, boron (B) or the like may beadded. After that, an insulating film 611 and an insulating film 612covering the gate electrode and the like are formed. A dangling bond ofthe crystalline semiconductor film can be terminated by a hydrogenelement mixed into the insulating film 611 (and the insulating film612).

In order to improve planarity, an insulating film 615 and an insulatingfilm 616 may be formed as an interlayer insulating film. For theinsulating films 615 and 616, an organic material, an inorganicmaterial, or a stacked structure thereof can be used. The insulatingfilms 615 and 616 can be formed from a material selected from siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide,aluminum nitride, aluminum oxynitride, aluminum nitride oxide oraluminum oxide containing a larger amount of nitrogen content thanoxygen content, diamond like carbon (DLC), polysilazane, carboncontaining nitrogen (CN), PSG (phosphosilicate glass), BPSG(borophosphosilicate glass), alumina, and a substance containing anotherinorganic insulating material. As the organic material that may beeither photosensitive or nonphotosensitive, polyimide, acryl, polyamide,polyimide amide, resist, benzocyclobutene, a siloxane resin, or the likecan be used. It is to be noted that the siloxane resin corresponds to aresin including a Si—O—Si bond. Siloxane has a skeleton structure of abond of silicon (Si) and oxygen (O). As for a substituent, an organicgroup containing at least hydrogen (such as an alkyl group or aromatichydrocarbon) is used. As for a substituent, a fluoro group may be used.Further, as for a substituent, an organic group containing at leasthydrogen and a fluoro group may be used.

The pixel portion and the driver circuit area can be formed in anintegrated manner over the same substrate by using the crystallinesemiconductor film. In this case, the transistor in the pixel portionand the transistor in the driver circuit area 608 b are concurrentlyformed. The transistor used in the driver circuit area 608 b forms aCMOS circuit. Although a thin film transistor including a CMOS circuithas a GOLD structure, an LDD structure such as the transistor 622 may beemployed.

A structure of the thin film transistor in the pixel portion is notlimited to this embodiment mode, and the thin film transistor in thepixel portion may have a single-gate structure in which one channelformation region is formed, a double-gate structure in which two channelformation regions are formed, or a triple-gate structure in which threechannel formation regions are formed. A thin film transistor in theperipheral driver circuit area may have a single-gate structure, adouble-gate structure, or a triple-gate structure.

Further, a thin film transistor is not limited to the manufacturingmethod shown in this embodiment mode. The thin film transistor may havea top-gate structure (such as a forward stagger type), a bottom-gatestructure (such as an inverted staggered type), a dual-gate structure inwhich two gate electrode layers are arranged above and below a channelformation region through a gate insulating film, or some otherstructures.

Next, an insulating layer 631 referred to as an orientation film isformed by a printing method or a spin coating method so as to cover thepixel electrode layer 630 and the insulating film 616. The insulatinglayer 631 can be selectively formed when a screen printing method or anoff-set printing method is used. After that, rubbing treatment isperformed. When a liquid crystal mode, for example, a VA mode, isemployed, there are cases when rubbing treatment is not performed. Aninsulating layer 633 serving as an orientation film is similar to theinsulating layer 631. Subsequently, the sealant 692 is formed in theperipheral region where the pixel is formed by a droplet dischargingmethod.

Then, the opposite substrate 695 provided with the insulating layer 633serving as an orientation film, a conductive layer 634 serving as anopposite electrode, and a colored layer 635 serving as a color filterare attached to the substrate 600 that is a TFT substrate through aspacer 637. A liquid crystal layer 632 is provided in a space betweenthe substrate 600 and the opposite substrate 695. After that, a firstlayer 641 including a polarizer and a second layer 642 including apolarizer are provided on an outer side of the opposite substrate 695. Athird layer 643 including a polarizer and a fourth layer 644 including apolarizer are provided on a side opposite to a surface having an elementof the substrate 600. The layer 643 including a polarizer and the layer644 including a polarizer are provided on a surface of the substrateopposite to the surface provided with an element. Filler may be mixedinto the sealant, and the opposite substrate 695 may be provided with ashielding film (black matrix) or the like. For a case of full-colordisplay of the liquid crystal display device, the color filter or thelike may be formed from a material emitting a red color (R), a greencolor (G), and blue color (B). For a case of mono-color display, thecolor filter or the like may be formed from a material emitting at leastone color.

When RGB light emitting diodes (LEDs) or the like are arranged in abacklight and a successive additive color mixture method (a fieldsequential method) that conducts color display by time division isemployed, there is a case when a color filter is not provided. The blackmatrix may also be provided to reduce the reflection of outside light bythe wires of the transistor and the CMOS circuit. Therefore, the blackmatrix is provided so as to be overlapped with the transistor and theCMOS circuit. It is to be noted the black matrix may also be provided soas to be overlapped with the capacitor element. This is because theblack matrix can prevent reflection due to a metal film forming thecapacitor element.

As a method for forming the liquid crystal layer, a dispenser method(dripping method) or a dipping method (pumping method) in which liquidcrystal is injected using a capillary phenomenon after attaching thesubstrate 600 having an element and the opposite substrate 695 may beused. A dripping method may be applied when a large-sized substrate towhich it is difficult to apply an injecting method is used.

A spacer may be provided in such a way that particles each having a sizeof several μ meters are sprayed. In this embodiment mode, a method isemployed in which a resin film is formed over the entire surface of thesubstrate and the resin film is subjected to an etching process. Thematerial of such a spacer is applied by a spinner and then light-exposedand developed so that a predetermined pattern is formed. Moreover, thespacer is heated at 150° C. to 200° C. in a clean oven or the like to behardened. The thus manufactured spacer can have various shapes dependingon the conditions of light exposure and development processes. It ispreferable that the spacer have a columnar shape with a flat top so thatmechanical intensity for the liquid crystal display device can besecured when the opposite substrate is attached. The shape can be conic,pyramidal, or the like without any particular limitation.

A connection portion is formed in order to connect an external wiringboard with the inside of the display device formed in accordance withthe above-described steps. An insulating layer in the connection portionis removed by ashing treatment using an oxygen gas under atmosphericpressure or near atmospheric pressure. This treatment uses an oxygen gasand one or more of hydrogen, CF₄, NF₃, H₂O, and CHF₃. In this step, theashing treatment is performed after sealing with the use of the oppositesubstrate in order to prevent damage or breaking due to staticelectricity. If the effect by static electricity is little, the ashingtreatment may be carried out at any timing.

Subsequently, a terminal electrode layer 678 electrically connected tothe pixel portion is provided with an FPC 694, which is a wiring boardfor connection, through an anisotropic conductive layer 696. The FPC 694is to transmit external signals or potential. Through the above steps, aliquid crystal display device having a display function can bemanufactured.

A wiring included in the transistor, the gate electrode layer, the pixelelectrode layer 630, and the conductive layer 634 that is an oppositeelectrode can be formed from a material selected from indium tin oxide(ITO), indium zinc oxide (IZO) in which zinc oxide (ZnO) is mixed withindium oxide, conductive materials in which silicon oxide (SiO₂) ismixed with indium oxide, organoindium, organotin, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, or indium tin oxide containingtitanium oxide; a metal such as tungsten (W), molybdenum (Mo), zirconium(Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum(Al), or copper (Cu); an alloy of such metals; or metal nitride thereof.

The substrate 600 is provided with a stacked layer of the third layer643 including a polarizer and the fourth layer 644 including apolarizer. The opposite substrate 695 is provided with a stacked layerof the first layer 641 including a polarizer and the second layer 642including a polarizer. The third layer 643 including a polarizer and thefourth layer 644 including a polarizer, which are provided on thebacklight side, are arranged to be in a parallel Nicols state. The firstlayer 641 including a polarizer and the second layer 642 including apolarizer, which are provided on the viewing side, are arranged so as todeviate from a parallel Nicols state. The absorption axes of thepolarizers of one of a pair of the stacked polarizers, preferably thestacked polarizer on the viewing side, are deviated, which is a featureof the present invention. Accordingly, the contrast ratio can beenhanced. In this embodiment mode, wavelength distributions ofextinction coefficients with respect to the absorption axes of the firstlayer 641 including a polarizer and the second layer 642 including apolarizer are different from each other. Similarly, wavelengthdistributions of extinction coefficients with respect to the absorptionaxes of the third layer 643 including a polarizer and the fourth layer644 including a polarizer are different from with each other.

The stacked layer of the third layer 643 including a polarizer and thefourth layer 644 including a polarizer and the stacked layer of thefirst layer 641 including a polarizer and the second layer 642 includinga polarizer are bonded to the substrate 600 and the opposite substrate695, respectively. A retardation film may be stacked to be interposedbetween the stacked layer including a polarizer and the substrate.

The stacked polarizers having different wavelength distributions ofextinction coefficients are provided so that the absorption axes thereofare arranged to be deviated from each other so as to deviate in such adisplay device, thereby the contrast ratio can be enhanced. In thepresent invention, a plurality of polarizers can be made a polarizerhaving a staked-layer structure, which is different from a structure inwhich a thickness of a polarizer is simply made thick. The stackedpolarizer deviates, thereby the contrast ratio can be enhanced ascompared with that of the structure in which a thickness is simply madethick.

This embodiment mode can be freely combined with the above embodimentmodes.

Embodiment Mode 7

In this embodiment mode, a liquid crystal display device using a thinfilm transistor that includes an amorphous semiconductor film inaddition to stacked layers each including a polarizer having a differentwavelength distribution of extinction coefficient from each other, whichis different from that of the above embodiment modes, will be explained.

A display device shown in FIG. 15 includes a transistor 220 that is aninversely staggered thin film transistor in a pixel portion, a pixelelectrode layer 201, an insulating layer 203, a liquid crystal layer204, a spacer 281, an insulating layer 205, an opposite electrode layer206, a color filter 208, a black matrix 207, an opposite substrate 210,a first layer 231 including a polarizer, a second layer 232 including apolarizer, a third layer 233 including a polarizer, and a fourth layer234 including a polarizer over a substrate 200. In addition, the displaydevice also includes a sealant 282, a terminal electrode layer 287, ananisotropic conductive layer 285, and an FPC 286 in a sealing region.

A gate electrode layer, a source electrode layer, and a drain electrodelayer of the transistor 220 that is the inversely staggered thin filmtransistor manufactured in this embodiment mode are formed by a dropletdischarging method. The droplet discharging method is a method fordischarging a composition containing a liquid conductive material andsolidifying the composition by drying and baking, thereby a conductivelayer and an electrode layer are formed. By discharging a compositioncontaining an insulating material and solidifying it by drying andbaking, an insulating layer can also be formed. By the dropletdischarging method, a constituent of a display device such as aconductive layer or an insulating layer can be selectively formed, whichcan simplify the manufacturing steps and reduce the loss of materials;thus, a display device can be manufactured at low cost with highproductivity.

In this embodiment mode, an amorphous semiconductor is used as asemiconductor layer, and a semiconductor layer having one conductivitymay be formed as needed. In this embodiment mode, a semiconductor layerand an n-type amorphous semiconductor layer as a semiconductor layerhaving one conductivity are stacked. Further, an NMOS structure of ann-channel thin film transistor in an n-type semiconductor layer, a PMOSstructure of a p-channel thin film transistor in which a p-typesemiconductor layer is formed, or a CMOS structure of an n-channel thinfilm transistor and a p-channel thin film transistor can bemanufactured. In this embodiment mode, the transistor 220 is ann-channel inversely staggered thin film transistor. Furthermore, achannel protective-type inversely staggered thin film transistorprovided with a protective layer over a channel region of thesemiconductor layer can be used.

In addition, in order to impart conductivity, an n-channel thin filmtransistor and a p-channel thin film transistor can also be formed byadding an element imparting conductivity by doping and forming animpurity region in the semiconductor layer. Instead of forming then-type semiconductor layer, conductivity may be imparted to thesemiconductor layer by performing plasma treatment with a PH₃ gas.

A semiconductor can be formed using an organic semiconductor material bya printing method, a spray method, a spin coating method, a dropletdischarging method, a dispenser method, or the like. In this case, sincethe above etching step is not necessary, the number of steps can bereduced. As an organic semiconductor, a low molecular organic material,a high molecular organic material, an organic coloring matter, aconductive high molecular organic material, or the like can be employed.A π-conjugated high molecular material with the skeleton includingconjugated double bonds is desirably used as an organic semiconductormaterial in the present invention. Typically, a soluble high molecularmaterial such as polythiophene, polyfluorene, poly(3-alkyl thiophene), apolythiophene derivative, or pentacene can be used.

Next, a structure of a backlight unit 352 is explained. The backlightunit 352 includes a cold cathode tube, a hot cathode tube, a lightemitting diode, an inorganic EL, or an organic EL as a light source 331that emits light, a lamp reflector 332 to effectively lead light to alight conducting plate 335, the light conducting plate 335 by whichlight is totally reflected and light is led to the entire surface of thedisplay panel, a diffusing plate 336 for reducing variations inbrightness, and a reflector plate 334 for reusing light leaked under thelight conducting plate 335.

A control circuit for controlling the luminance of the light source 331is connected to the backlight unit 352. The luminance of the lightsource 331 can be controlled by a signal supplied from the controlcircuit.

A stacked layer of the third layer 233 including a polarizer and thefourth layer 234 including a polarizer are provided between thesubstrate 200 and the backlight unit 352. A stacked layer of the firstlayer 231 including a polarizer and the second layer 232 including apolarizer are stacked on the opposite substrate 210. The third layer 233including a polarizer and the fourth layer 234 including a polarizer,which are provided on the backlight side, are arranged to be in aparallel Nicols state. The first layer 231 including a polarizer and thesecond layer 232 including a polarizer, which are provided on theviewing side, are arranged so as to deviate from a parallel Nicolsstate. In such a structure, one of a pair of the stacked layers eachincluding a polarizer, preferably the stacked polarizers on the viewingside are deviated, which is a feature of the present invention.Accordingly, the contrast ratio can be enhanced. In this embodimentmode, wavelength distributions of extinction coefficients with respectto absorption axes of the first layer 231 including a polarizer and thesecond layer 232 including a polarizer are different from each other.Similarly, wavelength distributions of extinction coefficients withrespect to absorption axes of the third layer 233 including a polarizerand the fourth layer 234 including a polarizer are different from eachother.

The stacked layer of the third layer 233 including a polarizer and thefourth layer 234 including a polarizer and the stacked layer of thefirst layer 231 including a polarizer and the second layer 232 includinga polarizer are bonded to the substrate 200 and the opposite substrate210, respectively. Further, a retardation film may be stacked to beinterposed between the stacked layer including a polarizer and thesubstrate.

The stacked polarizers having different wavelength distributions ofextinction coefficients are provided and arranged so that the absorptionaxes thereof are deviated in such a liquid crystal display device,thereby the contrast ratio can be enhanced. In the present invention, aplurality of polarizers can be made a layer including polarizer having astaked-layer structure, which is different from a structure in which athickness of a polarizer is simply made thick. The stacked polarizerdeviates, thereby the contrast ratio can be enhanced as compared withthat of the structure in which a thickness is simply made thick.

This embodiment mode can be freely combined with the above embodimentmodes.

Embodiment Mode 8

In this embodiment mode, operation of each circuit or the like includedin a display device will be explained.

FIG. 24A shows a system block view of a pixel portion 505 and a drivercircuit portion 508 of a display device.

In the pixel portion 505, a plurality of pixels is included, and aswitching element is provided in each intersection region of a signalline 512 and a scanning line 510 that becomes a pixel. By the switchingelements, application of a voltage to control tilt of liquid crystalmolecules can be controlled. Such a structure where switching elementsare provided in each intersecting region is referred to as an activetype. The pixel portion of the present invention is not limited to suchan active type, and may have a passive type structure instead. Thepassive type can be formed by a simple process because each pixel doesnot have a switching element.

The driver circuit portion 508 includes a control circuit 502, a signalline driver circuit 503, and a scanning line driver circuit 504. Thecontrol circuit 502 has a function to control a gray scale in accordancewith display contents of the pixel portion 505. Therefore, the controlcircuit 502 inputs a signal generated to the signal line driver circuit503 and the scanning line driver circuit 504. When a switching elementis selected through a scanning line 510 in accordance with the scanningline driver circuit 504, a voltage is applied to a pixel electrode in aselected intersecting region. The value of this voltage is determinedbased on a signal inputted from the signal line driver circuit 503through the signal line.

Further, in the control circuit 502, a signal controlling electric powersupplied to a lighting unit 506 is generated, and the signal is inputtedto a power supply 507 of the lighting unit 506. The backlight unit shownin the above embodiment mode can be used for the lighting unit. It is tobe noted that the lighting unit includes a front light besides abacklight. A front light is a platy light unit formed of an illuminantand a light conducting body, which is attached to a front side of apixel portion and illuminates the whole place. By such a lighting unit,the pixel portion can be evenly illuminated with low power consumption.

As shown in FIG. 24B, the scanning line driver circuit 504 includescircuits serving as a shift register 541, a level shifter 542, and abuffer 543. Signals such as a gate start pulse (GSP) and a gate clocksignal (GCK) are inputted to the shift register 541. It is to be notedthat the scanning line driver circuit of the present invention is notlimited to the structure shown in FIG. 24B.

Further, as shown in FIG. 24C, the signal line driver circuit 503includes circuits serving as a shift register 531, a first latch 532, asecond latch 533, a level shifter 534, and a buffer 535. The circuitserving as the buffer 535 is a circuit having a function for amplifyinga weak signal and includes an operational amplifier and the like.Signals such as start pulses (SSP) are inputted to the level shifter534, and data (DATA) such as video signals is inputted to the firstlatch 532. Latch (LAT) signals can be temporarily held in the secondlatch 533, and are inputted to the pixel portion 505 concurrently. Thisoperation is referred to as a line sequential drive. Therefore, a pixelthat performs not a line sequential drive but a dot sequential drivedoes not require the second latch. Thus, the signal line driver circuitof the present invention is not limited to the structure shown in FIG.24C.

The signal line driver circuit 503, the scanning line driver circuit504, and the pixel portion 505 as described above can be formed ofsemiconductor elements provided over one substrate. The semiconductorelement can be formed using a thin film transistor provided over a glasssubstrate. In this case, a crystalline semiconductor film may be appliedto the semiconductor element (refer to Embodiment Mode 5). A crystallinesemiconductor film can constitute a circuit included in a driver circuitportion because it has a high electrical characteristic, in particular,mobility. Further, the signal line driver circuit 503 and the scanningline driver circuit 504 may be mounted on a substrate by using an IC(Integrated Circuit) chip. In this case, an amorphous semiconductor filmcan be applied to a semiconductor element in a pixel portion (refer toEmbodiment Mode 7).

In such a display device, stacked polarizers having different wavelengthdistributions of extinction coefficients are provided and arranged sothat their absorption axes are deviated from each other, thereby thecontrast ratio can be enhanced. In other words, the contrast ratio oflight from a lighting unit controlled by a control circuit can beenhanced.

Embodiment Mode 9

In this embodiment mode, a structure of a backlight will be explained. Abacklight is provided in a display device as a backlight unit having alight source. The light source is surrounded by a reflector plate sothat the backlight unit effectively scatters light.

As shown in FIG. 19A, a cold cathode tube 401 can be used as a lightsource in a backlight unit 352. In order to reflect light efficientlyfrom the cold cathode tube 401, a lamp reflector 332 can be provided.The cold cathode tube 401 is mostly used for a large-sized displaydevice due to the intensity of the luminance from the cold cathode tube.Therefore, the backlight unit having a cold cathode tube can be used fordisplay of a personal computer.

As shown in FIG. 19B, a light emitting diode (LED) 402 can be used as alight source in a backlight unit 352. For example, light emitting diodes(W) 402 emitting a white color are each arranged at predeterminedintervals. In order to reflect light efficiently from the light emittingdiode (W) 402, a lamp reflector 332 can be provided.

As shown in FIG. 19C, light emitting diodes (LED) 403, 404, and 405 eachemitting a color of RGB can be used as a light source in a backlightunit 352. When the light emitting diodes (LED) 403, 404, and 405emitting each color of RGB are used, a color reproduction property canbe enhanced as compared with a case when only the light emitting diode(W) 402 emitting a white color is used. In order to reflect lightefficiently from the light emission diode (W) 402, a lamp reflector 332can be provided.

As shown in FIG. 19D, when light emitting diodes (LED) 403, 404, and 405each emitting a color of RGB is used as a light source, it is notnecessary that the number and arrangement thereof is the same for all.For example, a plurality of light emitting diodes emitting a color thathas low light emitting intensity (such as green) may be arranged.

The light emitting diode 402 emitting a white color and the lightemitting diodes (LED) 403, 404, and 405 each emitting color of RGB maybe combined.

When a field sequential method is applied in a case of using the lightemitting diodes of RGB, color display can be performed by sequentiallylighting the light emitting diodes of RGB in accordance with the time.

The light emitting diode is suitable for a large-sized display devicebecause the luminance is high when the light emitting diode is used. Inaddition, a color reproduction property of the light emitting diode issuperior to that of a cold cathode tube because the color purity of eachcolor of RGB is favorable, and an area required for arrangement can bereduced. Therefore, a narrower frame can be achieved when the lightemitting diode is applied to a small-sized display device.

Further, a light source needs not provided as a backlight unit shown inFIGS. 19A to 19D. For example, when a backlight having a light emittingdiode is mounted on a large-sized display device, the light emittingdiode can be arranged on the back side of the substrate. In this case,each of the light emitting diodes can be sequentially arranged atpredetermined intervals. A color reproduction property can be enhancedin accordance with the arrangement of the light emitting diodes.

Stacked layers each including a polarizer are arranged so that theabsorption axes of the polarizers are deviated from each other andprovided in a display device using such a backlight, thereby an imagehaving a high contrast ratio can be provided. A backlight having a lightemitting diode is particularly suitable for a large-sized displaydevice, and an image having high quality can be provided even in a darkplace by enhancing the contrast ratio of the large-sized display device.

Embodiment Mode 10

Driving methods of a liquid crystal for a liquid crystal display deviceinclude a vertical electric field method where a voltage is appliedperpendicularly to a substrate and a horizontal electric field methodwhere a voltage is applied parallel to a substrate. The structure inwhich stacked layers each including polarizers are arranged so thattheir absorption axes are deviated can be applied to either the verticalelectric field method or the horizontal electric field method. In thisembodiment mode, various kinds of liquid crystal modes will beexplained, to which stacked layers each including polarizers that arearranged so that their absorption axes are deviated from each other canbe applied.

First, FIGS. 27(A1) and 27(A2) each show a schematic diagram of a liquidcrystal display device of a TN mode.

Similar to the above embodiment modes, a layer 100 including a displayelement is interposed between a first substrate 101 and a secondsubstrate 102, which are arranged to be opposite to each other. A firstlayer 103 including a polarizer and a second layer 102 including apolarizer are arranged so as to deviate from a parallel Nicols state onthe first substrate 101 side. A third layer 105 including a polarizerand a fourth layer 106 including a polarizer are arranged to be in aparallel Nicols state on the second substrate 102 side. The first layer103 including a polarizer and the third layer 105 including a polarizerare arranged to be in a crossed Nicols state.

Although not shown, a backlight or the like is arranged on an outer sideof the fourth layer 106 including a polarizer. A first electrode 108 anda second electrode 109 are respectively provided over the firstsubstrate 101 and the second substrate 102. The first electrode 108 on aside opposite to the backlight, in other words, on the viewing side, isformed so as to have at least a light transmitting property.

When a liquid crystal display device having such a structure is in anormally white mode, when a voltage is applied to the first electrode108 and the second electrode 109 (referred to as a vertical electricfield method), black display is performed as shown in FIG. 27(A1). Atthat time, liquid crystal molecules are aligned vertically. Thus, lightfrom the backlight cannot pass through the substrate, which leads toblack display.

As shown in FIG. 27(A2), when a voltage is not applied between the firstelectrode 108 and the second electrode 109, white display is performed.At that time, liquid crystal molecules are aligned horizontally whiletwisted on a plane. As a result, light from the backlight can passthrough the substrate provided with a stacked layer including apolarizer that is arranged on the viewing side so as to deviate from aparallel Nicols state, which is a pair of the stacked layers including apolarizer, thereby a predetermined image is displayed.

By providing a color filter at that time, full-color display can beperformed. The color filter can be provided on either the firstsubstrate 101 side or the second substrate 102 side.

A known material may be used for a liquid crystal material of the TNmode.

FIG. 27(B1) shows a schematic diagram of a liquid crystal display deviceof a VA mode. A VA mode is a mode where liquid crystal molecules arealigned perpendicularly to a substrate when there is no electric field.

Similarly to FIGS. 27(A1) and 27(A2), a first electrode 108 and a secondelectrode 109 are respectively provided over a first substrate 101 and asecond substrate 102. In addition, the first electrode 108 on a sideopposite to the backlight, in other words, on the viewing side, isformed so as to have at least a light transmitting property. A firstlayer 103 including a polarizer and a second layer 104 including apolarizer are arranged so as to deviate from a parallel Nicols state.Further, on the second substrate 102 side, a third layer 105 including apolarizer and a fourth layer 106 including a polarizer are arranged tobe in a parallel Nicols state. The first layer 103 including a polarizerand the third layer 105 including a polarizer are arranged to be in acrossed Nicols state.

When a voltage is applied to the first electrode 108 and the secondelectrode 109 (vertical electric field method) in a liquid crystaldisplay device having such a structure, white display is performed,which means an on state, as shown in FIG. 27(B1). At that time, liquidcrystal molecules are aligned horizontally. Thus, light from thebacklight can pass through the substrate provided with the stackedlayers each including a polarizer that are deviated from a parallelNicols state, thereby a predetermined image is displayed. By providing acolor filter at that time, full-color display can be performed. Thecolor filter can be provided on either the first substrate 101 side orthe second substrate 102 side.

As shown in FIG. 27(B2), when no voltage is applied between the firstelectrode 108 and the second electrode 109, black display is performed,which means an off state. At that time, liquid crystal molecules arealigned vertically. Thus, light from the backlight cannot pass throughthe substrate, which leads to black display.

Thus, in an off state, liquid crystal molecules are perpendicular to thesubstrate, thereby black display is performed. Meanwhile, in an onstate, liquid crystal molecules are parallel to the substrate, therebywhite display is performed. In an off state, liquid crystal moleculesrise; therefore, polarized light from the backlight passes through acell without being affected by the liquid crystal molecules and can becompletely blocked by the layer including a polarizer on the oppositesubstrate side. Accordingly, at least one of the layers including astacked polarizer of a pair of the layers including a stacked polarizeris arranged so as to deviate from a parallel Nicols state, therebyfurther enhancement of the contrast ratio can be assumed.

FIGS. 27(C1) and 27(C2) show an example in which a stacked layerincluding a polarizer of the present invention is applied to an MVA modewhere alignment of liquid crystal is divided. The MVA mode is a methodin which one pixel is divided into a plurality and the viewing angledependency for each portion is compensated for that of other portions.As shown in FIG. 27(C1), projections 158 and 159, the cross-section ofeach of which is a triangle shape, are respectively provided on a firstelectrode 108 and a second electrode 109. When a voltage is applied tothe first electrode 108 and the second electrode 109 (vertical electricfield method), white display is performed, which means an on state, asshown in FIG. 27(C1). At that time, liquid crystal molecules are alignedso as to tilt toward the projections 158 and 159. Thus, light from thebacklight can pass through the substrate provided with the stackedlayers each including a polarizer that are deviated from a parallelNicols state, thereby predetermined image display can be performed. Byproviding a color filter at that time, full-color display can beperformed. The color filter can be provided on either the firstsubstrate 101 side or the second substrate 102 side.

As shown in FIG. 27(C2), when a voltage is not applied between the firstelectrode 108 and the second electrode 109, black display is performed,which means an off state. At that time, liquid crystal molecules arealigned vertically. Thus, light from the backlight cannot pass throughthe substrate, which leads to black display.

FIGS. 30A and 30B show a top view and a cross-sectional view of anotherexample of an MVA mode. In FIG. 30A, a second electrode is formed into abent pattern of a dog-legged shape to be second electrodes 109 a, 109 b,and 109 c. An insulating layer 162 that is an orientation film is formedover the second electrodes 109 a, 109 b, and 109 c. As shown in FIG.30B, a projection 158 is formed over a first electrode 108 to have ashape corresponding to that of the second electrodes 109 a, 109 b, and109 c. Openings of the second electrodes 109 a, 109 b, and 109 c serveas projections, which can move the liquid crystal molecules.

FIGS. 28(A1) and 28(A2) each show a schematic diagram of a liquidcrystal display device of an OCB mode. In the OCB mode, alignment ofliquid crystal molecules forms a compensation state optically in aliquid crystal layer, which is referred to as a bent orientation.

Similarly to FIGS. 27(A1) to 27(C2), a first electrode 108 and a secondelectrode 109 are respectively provided on a first substrate 101 and asecond substrate 102. Although not shown, a backlight or the like isarranged on an outer side of a fourth layer 106 including a polarizer.In addition, the first electrode 108 on a side opposite to thebacklight, in order words, on the viewing side, is formed so as to haveat least a light transmitting property. A first layer 103 including apolarizer and a second layer 104 including a polarizer are arranged soas to deviate from a parallel Nicols state. A third layer 105 includinga polarizer and the fourth layer 106 including a polarizer are arrangedon the second substrate 102 side so as to be in a parallel Nicols state.The first layer 103 including a polarizer and the third layer 105including a polarizer are arranged so as to be in a crossed Nicolsstate.

When a constant on-voltage is applied to the first electrode 108 and thesecond electrode 109 (vertical electric field method) in a liquidcrystal display device having such a structure, black display isperformed as shown in FIG. 28(A1). At that time, liquid crystalmolecules are aligned vertically. Thus, light from the backlight cannotpass through the substrate, which leads to black display.

When a constant off-voltage is applied between the first electrode 108and the second electrode 109, white display is performed as shown inFIG. 28(A2). At that time, liquid crystal molecules are aligned in abent orientation. Thus, light from the backlight can pass through thesubstrate provided with the stacked layer including a polarizer, therebya predetermined image is displayed. By providing a color filter at thattime, full-color display can be performed. The color filter can beprovided on either the first substrate 101 side or the second substrate102 side.

In such an OCB mode, a stacked layer including a polarizer, which is apair of the stacked layers including a polarizer, on the viewing side isarranged so as to deviate from a parallel Nicols state, therebybirefringence caused in a liquid crystal layer can be compensated. As aresult, the contrast ratio and a wide viewing angle can be enhanced.

FIGS. 28(B1) and (B2) each show a schematic diagram of an FLC mode andan AFLC mode.

Similarly to FIGS. 27(A1) to 27(C2), a first electrode 108 and a secondelectrode 109 are respectively provided on a first substrate 101 and asecond substrate 102. The first electrode 108 on a side opposite to abacklight, in other words, on a viewing side is formed to have at leasta light transmitting property. A first layer 103 including a polarizerand a second layer 104 including a polarizer are arranged so as todeviate from a parallel Nicols state. A third layer 105 including apolarizer and a fourth layer 106 including a polarizer are arranged onthe second substrate 102 side so as to be in a parallel Nicols state.The first layer 103 including a polarizer and the third layer 105including a polarizer are arranged so as to be in a crossed Nicolsstate.

When a voltage is applied to the first electrode 108 and the secondelectrode 109 (referred to as vertical electric field method) in aliquid crystal display device having such a structure, white display isperformed as shown in FIG. 28(B1). At that time, liquid crystalmolecules are aligned horizontally while rotated on a plane surface.Thus, light from the backlight can pass through the substrate providedwith the stacked layer including a polarizer, which is a pair of thestacked layers including a polarizer, on the viewing side so as todeviate from a parallel Nicols state, thereby a predetermined image isdisplayed.

When no voltage is applied between the first electrode 108 and thesecond electrode 109, black display is performed as shown in FIG.28(B2). At that time, liquid crystal molecules are aligned horizontally.Thus, light from the backlight cannot pass through the substrate, whichleads to black display.

When a color filter is provided at that time, full-color display can beperformed. The color filter can be provided on either the firstsubstrate 101 side or the second substrate 102 side.

A known material may be used for a liquid crystal material of the FLCmode and the AFLC mode.

FIGS. 29(A1) and 29(A2) each shows a schematic diagram of a liquidcrystal display device of an IPS mode. In the IPS mode, liquid crystalmolecules are constantly rotated on a plane surface with respect to asubstrate, and a horizontal electric field method is applied to theelectrode provided on only one substrate side.

In the IPS mode, a liquid crystal is controlled by a pair of electrodesprovided on one substrate. Therefore, a pair of electrodes 150 and 151is provided over a second substrate 102. The pair of electrodes 150 and151 may each have a light transmitting property. A first layer 103including a polarizer and a second layer 104 including a polarizer arearranged so as to deviate from a parallel Nicols state. In addition, athird layer 105 including a polarizer and a fourth layer 106 including apolarizer are arranged on the second substrate 102 side so as to be in aparallel Nicols state. The first layer 103 including a polarizer and thethird layer 105 including a polarizer are arranged so as to be in acrossed Nicols state. Although not shown, a backlight or the like isarranged on an outer side of the fourth layer 106 including a polarizer.

When a voltage is applied to the pair of electrodes 150 and 151 in aliquid crystal display device having such a structure, white display isperformed, which means an on state, as shown in FIG. 29(A1). Thus, lightfrom the backlight can pass through the substrate provided with thestacked layer including a polarizer, which is one of a pair of thestacked layers including a polarizer, on the viewing side, whichdeviates from a parallel Nicols state, thereby a predetermined image isdisplayed.

By providing a color filter at that time, full-color display can beperformed. The color filter can be provided on either the firstsubstrate 101 side or on the second substrate 102 side.

When no voltage is applied between the pair of electrodes 150 and 151,black display is performed, which means an off state, as shown in FIG.29(A2). At that time, liquid crystal molecules are aligned horizontallywhile rotated on a plane surface. Thus, light from the backlight cannotpass through the substrate, which leads to black display.

FIGS. 25A to 25D each show an example of the pair of electrodes 150 and151 that can be used in the IPS mode. As shown in top views of FIGS. 25Ato 25D, the pair of electrodes 150 and 151 are alternatively formed. InFIG. 25A, electrodes 150 a and 151 a have an undulating wave shape. InFIG. 25B, electrodes 150 b and 151 b have a concentric circular opening.In FIG. 25C, electrodes 150 c and 151 c have a comb-like shape and arepartially overlapped with each other. In FIG. 25D, electrodes 150 d and151 d have a comb-like shape in which the electrodes are meshed witheach other.

An FFS mode can be used instead of the IPS mode. The FFS mode has astructure in which a pair of electrodes are not formed in the samelayer, and an electrode 153 is formed over an electrode 152 with aninsulating film interposed therebetween as shown in FIGS. 29(B1) and29(B2), while the pair of electrodes are formed on the same surface inthe IPS mode.

When a voltage is applied to the pair of electrodes 152 and 153 in aliquid crystal display device having such a structure, white display isperformed, which means an on state, as shown in FIG. 29(B1). Thus, lightfrom a backlight can pass through the substrate provided with thestacked layer including a polarizer on the viewing side that deviatesfrom a parallel Nicols state, which is one of a pair of layers includinga stacked polarizer, thereby a predetermined image is displayed.

By providing a color filter at that time, full-color display can beperformed. The color filter can be provided on either the firstsubstrate 101 side or on the second substrate 102 side.

When no voltage is applied between the pair of electrodes 152 and 153,black display is performed, which means an off state, as shown in FIG.29(B2). At that time, liquid crystal molecules are aligned horizontallywhile rotated on a plane surface. Thus, light from the backlight cannotpass through the substrate, which leads to black display.

FIGS. 26A to 26D each show an example of the pair of electrodes 152 and153 that can be used in the FFS mode. As shown in top views of FIGS. 26Ato 26D, the electrodes 153 that are formed into various patterns areformed over the electrodes 152. In FIG. 26A, an electrode 153 a over anelectrode 152 a has a bent dog-legged shape. In FIG. 26B, an electrode153 b over an electrode 152 b has a concentric circular shape. In FIG.26C, an electrode 153 c over an electrode 152 c has a comb-like shape inwhich the electrodes are messed with other. In FIG. 26D, an electrode153 d over an electrode 152 d has a comb-like shape.

A known material may be used for a liquid crystal material of the IPSmode and the FFS mode.

A structure in which a stacked layer including a polarizer on theviewing side, which is one of a pair of stacked layers including apolarizer of the present invention, is arranged so as to deviate from aparallel Nicols state is applied to a liquid crystal display device of avertical electric field method, thereby display with an even highercontrast ratio can be performed. Such a vertical electric field methodis suitable for a display device for a computer that is used in a roomor for a large-sized television.

Further, when the present invention is applied to a liquid crystaldisplay device of a horizontal electric field method, display with ahigh contrast ratio can be performed in addition to one with a viewingangle. Such a horizontal electric field method is suitable for aportable display device.

Furthermore, the present invention can be applied to a liquid crystaldisplay device of a rotation mode, a scattering mode, or a birefringencemode and a display device in which layers including a polarizer arearranged on both sides of the substrate.

This embodiment mode can be freely combined with the above embodimentmodes.

Embodiment Mode 11

This embodiment mode will be explained with reference to FIGS. 18A and18B. FIGS. 18A and 18B show an example of forming a display device (aliquid crystal display module) using a TFT substrate 2600 that ismanufactured by applying the present invention.

FIG. 18A shows an example of a liquid crystal display module where theTFT substrate 2600 and an opposite substrate 2601 are bonded with asealant 2602, and a pixel portion 2603 including a TFT or the like and aliquid crystal layer 2604 are provided therebetween so as to form adisplay region. A colored layer 2605 is necessary for color display. Fora case of an RGB method, colored layers corresponding to each color ofred, green, and blue are provided to correspond to each pixel. A firstlayer 2606 including a polarizer and a second layer 2626 including apolarizer are arranged on an outer side of the opposite substrate 2601.A third layer 2607 including a polarizer, a fourth layer 2627 includinga polarizer, and a lens film 2613 are arranged on an outer side of theTFT substrate 2600. A light source includes a cold cathode tube 2610 anda reflector plate 2611. A circuit board 2612 is connected to the TFTsubstrate 2600 through a flexible wiring board 2609. External circuitssuch as a control circuit and a power supply circuit are included.

Stacked layers of the third layer 2607 including a polarizer and thefourth layer 2627 including a polarizer which have different wavelengthdistributions of extinction coefficients from each other are providedbetween the TFT substrate 2600 and a backlight that is the light source.The stacked layers of the first layer 2606 including a polarizer and thesecond layer 2626 including a polarizer which have different wavelengthdistributions of extinction coefficients from each other are providedover the opposite substrate 2601. The third layer 2607 including apolarizer and the fourth layer 2627 including a polarizer, which areprovided on the backlight side, are arranged so as to be in a parallelNicols state. The first layer 2606 including a polarizer and the secondlayer 2626 including a polarizer, which are provided on the viewingside, are arranged so as to be deviated from a parallel Nicols state. Insuch a structure, one of a pair of the stacked layers each includingpolarizers having different wavelength distributions of extinctioncoefficients from each other, preferably the stacked layers eachincluding a polarizer on the viewing side are deviated. Accordingly, thecontrast ratio can be enhanced.

The stacked layer of the third layer 2607 including a polarizer and thefourth layer 2627 including a polarizer is bonded to the TFT substrate2600. The stacked layer of the first layer 2606 including a polarizerand the second layer 2626 including a polarizer are bonded to theopposite substrate 2601. In addition, a retardation film may be stackedto be interposed between the stacked layer including a polarizer and thesubstrate.

For the liquid crystal display module, a TN (Twisted Nematic) mode, anIPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching) mode, anMVA (Multi-domain Vertical Alignment) mode, an ASM (Axially Symmetricaligned Micro-cell) mode, an OCB (Optical Compensated Birefringence)mode, an FLC (Ferroelectric Liquid Crystal) mode, or the like can beused.

FIG. 18B shows an example of an FS-LCD (Field Sequential-LCD) in whichan OCB mode is applied to the liquid crystal display module of FIG. 18A.The FS-LCD emits red light, green light, and blue light during one frameperiod and can perform color display by combining images using timedivision. Since each light is emitted by a light emitting diode, a coldcathode tube, or the like, a color filter is not necessary. Thus, it isnot necessary to arrange color filters of three primary colors andrestrict the display region of each color, and color display of allthree colors can be performed in any regions; therefore, nine times asmany pixels can be displayed in the same area. On the other hand, sincethree colors of light are emitted during one frame period, high-speedresponse is required for a liquid crystal. By employing an FS method, anFLC mode, and an OCB mode to a display device of the present invention,a display device or a liquid crystal television device with highperformance and high image quality can be completed.

A liquid crystal layer in the OCB mode has a so-called π-cell structure.In the π-cell structure, liquid crystal molecules are oriented so thattheir pretilt angles are plane-symmetric along a center plane between anactive matrix substrate and an opposite substrate. An orientation stateof a π-cell structure becomes sprayed orientation when a voltage is notapplied between the substrates and shifts to bent orientation when avoltage is applied therebetween. When a voltage is applied further,liquid crystal molecules of bent orientation get orientatedperpendicular to the both substrates so that light is not transmitted.With the OCB mode, response with about 10 times higher speed than aconventional TN mode can be achieved.

Moreover, as a mode corresponding to the FS method, an SS-FLC or anHV-FLC using a ferroelectric liquid crystal (FLC) capable of high-speedoperation, or the like can also be used. The OCB mode uses a nematicliquid crystal having relatively low viscosity, while the HV-FLC or theSS-FLC uses a smectic liquid crystal. A material of an FLC, a nematicliquid crystal, a smectic liquid crystal, or the like can be used as theliquid crystal material.

Moreover, optical response speed of a liquid crystal display module getshigher by narrowing the cell gap of the liquid crystal display module.In addition, the optical response speed can also get higher bydecreasing the viscosity of the liquid crystal material. The increase inresponse speed is particularly advantageous when a pixel in a pixelportion of a liquid crystal display module of a TN mode or a dot pitchis less than or equal to 30 μm.

FIG. 18B shows a transmissive liquid crystal display module, in which ared light source 2910 a, a green light source 2910 b, and a blue lightsource 2910 c are provided as light sources. The light sources areprovided with a control portion 2912 in order to switch the red lightsource 2910 a, the green light source 2910 b, and the blue light source2910 c. The control portion 2912 controls light emission of each color,so that light enters the liquid crystal to combine images by timedivision, thereby performing color display.

Thus, absorption axes of the polarizers included in the layers aredeviated from a parallel Nicols state, thereby light leakage in theabsorption axis direction can be reduced. Therefore, the contrast ratioof the display device can be enhanced. A display device with highperformance and high image quality can be manufactured.

This embodiment mode can be used by being freely combined with the aboveembodiment modes.

Embodiment Mode 12

This embodiment mode will be explained with reference to FIG. 23. FIG.23 shows an example of forming a display device using a substrate 813that is a TFT substrate manufactured by applying the present invention.

FIG. 23 shows a display device portion 801 and a backlight unit 802. Thedisplay device portion 801 includes the substrate 813, a pixel portion814 including a TFT or the like, a liquid crystal layer 815, an oppositesubstrate 816, a first layer 817 including a polarizer, a second layer818 including a polarizer, a third layer 811 including a polarizer, afourth layer 812 including a polarizer, a slit (lattice) 850, a drivercircuit 819, and an FPC 837. The backlight unit 802 includes a lightsource 831, a lamp reflector 832, a reflector plate 834, a lightconducting plate 835, and a light diffuser plate 836.

The display device of the present invention shown in FIG. 23 makes itpossible to perform three-dimensional display without any need forspecial equipment such as glasses. The slit 850 with an opening that isarranged on the backlight unit side transmits light that is incidentfrom the light source and made to be a striped shape. Then, the light isincident on the display device portion 801. This slit 850 can makeparallax in both eyes of a viewer on the viewing side. The viewer seesonly a pixel for the right eye with the right eye and only a pixel for aleft eye with a left eye simultaneously. Therefore, the viewer can seethree-dimensional display. That is, in the display device portion 801,light given a specific viewing angle by the slit 850 passes through eachpixel corresponding to an image for the right eye and an image for theleft eye, thereby the image for the right eye and the image for the lefteye are separated into different viewing angles, and three-dimensionaldisplay is performed.

The third layer 811 including a polarizer and the fourth layer 812including a polarizer are provided and stacked between the substrate 813and the backlight that is the light source. The first layer 817including a polarizer and the second layer 818 including a polarizer areprovided and stacked over the opposite substrate 816. The third layer811 including a polarizer and the fourth layer 812 including a polarizerwhich have different wavelength distributions of extinction coefficientsfrom each other, which are provided on the backlight side, are arrangedso as to be in a parallel Nicols state. The first layer 817 including apolarizer and the second layer 818 including a polarizer which havedifferent wavelength distributions of extinction coefficients from eachother, which are provided on the viewing side, are arranged so as todeviate from a parallel Nicols state. In such a structure, one of a pairof the layers including a stacked polarizer, preferably, the stackedpolarizer on the viewing side, has a polarizer that deviates. Thus, evenslight light leakage can be prevented and the contrast ratio can beenhanced.

An electronic device such as a television device or a cellular phone ismanufactured with the use of a display device of the present invention,thereby an electronic device with high performance and high imagequality, which can perform three-dimension display, can be provided.

Embodiment Mode 13

By a display device formed by the present invention, a television device(also, referred to as a television simply or a television receiver) canbe completed. FIG. 20 shows a block diagram of a main structure of atelevision device. As for a display panel, any modes of the followingmay be employed: as the structure shown in FIG. 16A, a case where only apixel portion 701 is formed and a scanning line driver circuit 703 and asignal line driver circuit 702 are mounted by a TAB method as shown inFIG. 17B; a case where only the pixel portion 701 is formed and thescanning line driver circuit 703 and the signal line driver circuit 702are mounted by a COG method as shown in FIG. 17A; a case where a TFT isformed as shown in FIG. 16B, the pixel portion 701 and the scanning linedriver circuit 703 are formed over the same substrate, and the signalline driver circuit 702 is independently mounted as a driver IC; a casewhere the pixel portion 701, the signal line driver circuit 702, and thescanning line driver circuit 703 are formed over the same substrate asshown in FIG. 17C; and the like.

In addition, as another structure of an external circuit, a video signalamplifier circuit 705 that amplifies a video signal among signalsreceived by a tuner 704, a video signal processing circuit 706 thatconverts the signals output from the video signal amplifier circuit 705into chrominance signals corresponding to each colors of red, green, andblue, a control circuit 707 that converts the video signal into an inputspecification of a driver IC, or the like are provided on an input sideof the video signal. The control circuit 707 outputs signals to both ascanning line side and a signal line side. In a case of digital driving,a signal dividing circuit 708 may be provided on the signal line sideand an input digital signal may be divided into m pieces to be supplied.

An audio signal among signals received by the tuner 704 is transmittedto an audio signal amplifier circuit 709 and is supplied to a speaker713 through an audio signal processing circuit 710. A control circuit711 receives control information of a receiving station (receptionfrequency) or sound volume from an input portion 712 and transmitssignals to the tuner 704 or the audio signal processing circuit 710.

Such liquid crystal display modules are incorporated into each chassisas shown in FIGS. 21A to 21C, thereby a television device can becompleted. When a liquid crystal display module shown in FIGS. 18A and18B are used, a liquid crystal television device can be completed. Whena display device having a three-dimension display function as EmbodimentMode 11 is used, a television device that can perform three-dimensiondisplay can be manufactured. A main screen 2003 is formed by a displaymodule, and a speaker portion 2009, an operation switch, and the likeare provided as accessory equipment. In such a manner, a televisiondevice can be completed by the present invention.

As shown in FIG. 21A, a display panel 2002 is incorporated in a chassis2001, and general TV broadcast can be received by a receiver 2005. Inaddition, by connecting to a communication network by wired or wirelessconnections via a modem 2004, one-way (from a sender to a receiver) ortwo-way (between a sender and a receiver or between receivers)information communication can be carried out. The television device canbe operated by using a switch built in the chassis or a remote controlunit 2006. A display portion 2007 for displaying output information mayalso be provided in the remote control unit 2006.

Further, the television device may include a sub-screen 2008 formedusing a second display panel to display channels, volume, or the like,in addition to the main screen 2003. In this structure, the main screen2003 and the sub-screen 2008 can be formed using a liquid crystaldisplay panel of the present invention. The main screen 2003 may beformed using an EL display panel having a superior viewing angle, andthe sub-screen 2008 may be formed using a liquid crystal display panelcapable of displaying sub-images with lower power consumption. In orderto reduce the power consumption preferentially, the main screen 2003 maybe formed using a liquid crystal display panel, and the sub-screen 2008may be formed using an EL display panel such that the sub-screen canflash on and off. By using the present invention, even when many TFTsand electronic parts are used with such a large-sized substrate, ahighly reliable display device can be formed.

FIG. 21B shows a television device having a large display portion with asize of, for example, 20 to 80 inches. The television device includes achassis 2010, a display portion 2011, a keyboard portion 2012 that is anoperation portion, a speaker portion 2013, and the like. The presentinvention is applied to the manufacturing of the display portion 2011.The display portion of FIG. 21B uses a substance capable of being bent,and therefore, the television device has a bent display portion. Sincethe shape of the display portion can be designed freely as describedabove, a television device having the desired shape can be manufactured.

FIG. 21C shows a television device having a large display portion with asize of, for example, 20 to 80 inches. The television device includes achassis 2030, a display portion 2031, a remote control unit 2032 that isan operation portion, a speaker portion 2033, and the like. The presentinvention is applied to the manufacturing of the display portion 2031.The television device shown in FIG. 21C is a wall-hanging type so doesnot require a large installation space.

Birefringence of liquid crystal changes depending on a temperature.Therefore, the polarization of light passing through the liquid crystalchanges, and a light leakage condition from a polarizer on the viewingside changes. As a result, a change in the contrast ratio is generateddepending on the temperature of the liquid crystal. It is desirable thata driving voltage be controlled so as to keep the contrast ratioconstant. In order to control the driving voltage, an element fordetecting the transmittance may be arranged and the driving voltage maybe controlled based on the detection results. As the element fordetecting the transmittance, a photosensor including an IC chip can beused. In the display device, an element for detecting the temperaturemay be arranged and the driving voltage may be controlled based on thedetection results and the change in the contrast ratio with respect tothe temperature of the liquid crystal element. As the element fordetecting the temperature, a temperature sensor including an IC chip canbe used. In this case, the element for detecting the transmittance andthe element for detecting the temperature are preferably arranged so asto be hidden in the chassis of the display device.

For example, the element for detecting the temperature may be arrangednear a liquid crystal display element in a display device of the presentinvention, which is mounted on the television devices shown in FIGS. 21Ato 21C, and then, information about the change in temperature of theliquid crystal may be fed back to a circuit for controlling the drivingvoltage. Since the element for detecting the transmittance is preferablyset in a position closer to the viewing side, the element may bearranged on a surface of the display screen to be covered with thechassis. Then, information about the change in the transmittance that isdetected may be fed back to the circuit for controlling the drivervoltage in a way similar to the information about the temperature.

The present invention can adjust the contrast ratio minutely bydisplacing absorption axes of stacked polarizers having differentwavelength distributions of extinction coefficients. Therefore, thepresent invention can deal with a slight deviation of the contrast ratiowith respect to the temperature of the liquid crystal, and an optimalcontrast ratio can be made. Thus, polarizers are stacked so that thepolarizers having different wavelength distributions of extinctioncoefficients are deviated from each other in advance so that an optimalcontrast ratio can be made depending on the conditions (inside oroutside of a room, climate, or the like) where the display device of thepresent invention is used, thereby a television device or an electronicdevice with high performance and high image quality display can beprovided.

As a matter of course, the present invention is not limited to thetelevision device. The present invention can be applied to variousapplications such as a monitor of a personal computer, particularlylarge-sized display media typified by an information display board attrain stations, airports, or the like, and an advertising display boardon the street.

Embodiment Mode 14

An electronic device of the present invention includes: a televisiondevice (also simply referred to as a TV or a television receiver), acamera such as a digital camera and a digital video camera, a mobilephone set (also simply referred to as a cellular phone set or a cellularphone), a portable information terminal such as a PDA, a portable gamemachine, a monitor for a computer, a computer, an audio reproducingdevice such as a car audio set, an image reproducing device providedwith a recording medium such as a home-use game machine, and the like.Specific examples thereof will be explained with reference to FIGS. 22Ato 22E.

A portable information terminal shown in FIG. 22A includes a main body9201, a display portion 9202, and the like. The display device of thepresent invention can be applied to the display portion 9202. Thus, aportable information terminal with a high contrast ratio can beprovided.

A digital video camera shown in FIG. 22B includes a display portion9701, a display portion 9702, and the like. The display device of thepresent invention can be applied to the display portion 9701. Thus, adigital video camera with a high contrast ratio can be provided.

A cellular phone set shown in FIG. 22C includes a main body 9101, adisplay portion 9102, and the like. The display device of the presentinvention can be applied to the display portion 9102. Thus, a cellularphone set with a high contrast ratio can be provided.

A portable television set shown in FIG. 22D includes a main body 9301, adisplay portion 9302, and the like. The display device of the inventioncan be applied to the display portion 9302. Thus, a portable televisionset with a high contrast ratio can be provided. The display device ofthe present invention can be applied to various types of television setsincluding a small-sized television mounted on a portable terminal suchas a cellular phone set, a medium-sized television that is portable, anda large-sized television (for example, 40 inches in size or more).

A portable computer shown in FIG. 22E includes a main body 9401, adisplay portion 9402, and the like. The display device of the presentinvention can be applied to the display portion 9402. Thus, a portablecomputer with a high contrast ratio can be provided.

By the display device of the present invention, an electronic devicewith a high contrast ratio can be provided.

Embodiment 1

In this embodiment, for a case of a transmission type liquid crystaldisplay device of a TN mode, the result of optical calculation will beexplained, in which polarizers each of which has a different wavelengthdistribution of extinction coefficient with respect to the absorptionaxis are stacked and the outermost polarizer on the viewing sidedeviates from a crossed Nicols state with respect to a polarizer on abacklight side. It is to be noted that the contrast ratio indicates theratio of transmittance in white display (also referred to as whitetransmittance) to transmittance in black display (also referred to asblack transmittance) (white transmittance/black transmittance).Transmittance in white display and transmittance in black display wereeach calculated, and then the contrast ratio was calculated.

As for the calculation in this embodiment, a liquid crystal opticalcalculation simulator LCD MASTER (made by Shintech Inc.) was used.Optical calculations of transmittance were conducted using the LCDMASTER. The optical calculations were conducted with a 2×2 matrixoptical calculation algorithm where the wavelength range is from 380 nmto 780 nm, in which multiple interference between elements was not takeninto account.

As shown in FIG. 31 and FIG. 32, optical arrangement of an opticalcalculation object has a structure in which a polarizer 1, a polarizer2, a retardation film B2, a retardation film A2, a glass substrate,liquid crystal, a glass substrate, a retardation film A1, a retardationfilm B1, a polarizer 2, and a polarizer 1 are sequentially stacked froma backlight. The polarizer 1 and the polarizer 2 on the backlight sideare polarizing plates having different wavelength distributions ofextinction coefficients and each absorption axis thereof is at an angleof 135 degrees, so that two polarizers are in a parallel Nicols state.The polarizer 2 and the polarizer 1 on the viewing side are polarizingplates having different wavelength distributions of extinctioncoefficients, and the angle of the absorption axis of the polarizer 2 onthe viewing side is 45 degrees so that the polarizer 2 is in a crossedNicols state with the polarizer 1 on the backlight side. First, in orderto calculate the angle of an absorption axis of the polarizer 1 on theviewing side at which the contrast ratio is the highest, calculation ofthe contrast ratio was performed when the angle of the absorption axisof the polarizer 1 on the viewing side was turned by 30 degrees to 50degrees. Here, when a voltage that was applied to the liquid crystal was0 V or 5 V, the contrast ratio indicates the ratio of transmittance of 0V (white) to transmittance of 5 V (black) (transmittance at 0V/transmittance at 5 V). It is to be noted that the calculation in thisembodiment was performed to obtain contrast ratio of light extracted tothe viewing side with respect to the luminance of the backlight.

Table 1 and Table 2 show property values of the polarizers 1 and 2respectively. A thickness of each polarizer was 30 μm. Table 3 showsbirefringence values of the liquid crystal and Table 4 shows otherproperty values and orientation state of the liquid crystal 1. Table 5shows physical property values and arrangement of the retardation filmA1 and the retardation film A2. Table 6 shows physical property valuesand arrangement of the retardation film B1 and the retardation film B2.Each of the retardation films A1, A2, B1, and B2 is a retardation filmhaving a negative uniaxial property.

TABLE 1 wavelength refraction index of refraction index of extinctioncoefficient of extinction coefficient of (nm) transmission axisabsorption axis direction transmission axis direction absorption axisdirection 380 1.5 1.5 0.00565 0.0092 390 1.5 1.5 0.002 0.0095 400 1.51.5 0.001 0.0093 410 1.5 1.5 0.0006 0.0095 420 1.5 1.5 0.0004 0.01 4301.5 1.5 0.0003 0.011 440 1.5 1.5 0.00029 0.0113 450 1.5 1.5 0.000260.0115 460 1.5 1.5 0.00024 0.0117 470 1.5 1.5 0.00022 0.0118 480 1.5 1.50.00021 0.012 490 1.5 1.5 0.0002 0.0119 500 1.5 1.5 0.000196 0.0123 5101.5 1.5 0.0002 0.01225 520 1.5 1.5 0.0002 0.0123 530 1.5 1.5 0.00020.01225 540 1.5 1.5 0.0002 0.0123 550 1.5 1.5 0.0002 0.012 560 1.5 1.50.0002 0.0116 570 1.5 1.5 0.0002 0.0113 580 1.5 1.5 0.0002 0.0112 5901.5 1.5 0.0002 0.0112 600 1.5 1.5 0.0002 0.012 610 1.5 1.5 0.0002 0.0115620 1.5 1.5 0.0002 0.011 630 1.5 1.5 0.0002 0.0106 640 1.5 1.5 0.00020.0103 650 1.5 1.5 0.0002 0.0102 660 1.5 1.5 0.0002 0.0101 670 1.5 1.50.0002 0.01005 680 1.5 1.5 0.0002 0.01002 690 1.5 1.5 0.00018 0.01 7001.5 1.5 0.00018 0.0099 710 1.5 1.5 0.00018 0.0091 720 1.5 1.5 0.000180.008 730 1.5 1.5 0.00018 0.0065 740 1.5 1.5 0.00018 0.0057 750 1.5 1.50.00016 0.005 760 1.5 1.5 0.00015 0.0042 770 1.5 1.5 0.00014 0.0035 7801.5 1.5 0.00012 0.003

TABLE 2 wavelength refraction index of refraction index of extinctioncoefficient of extinction coefficient of (nm) transmission axisabsorption axis direction transmission axis direction absorption axisdirection 380 1.5 1.5 0.00565 0.008 390 1.5 1.5 0.002 0.0082 400 1.5 1.50.001 0.0079 410 1.5 1.5 0.0006 0.0079 420 1.5 1.5 0.0004 0.0077 430 1.51.5 0.0003 0.0079 440 1.5 1.5 0.00029 0.008 450 1.5 1.5 0.00026 0.0085460 1.5 1.5 0.00024 0.0086 470 1.5 1.5 0.00022 0.0087 480 1.5 1.50.00021 0.0096 490 1.5 1.5 0.0002 0.0095 500 1.5 1.5 0.000196 0.0095 5101.5 1.5 0.0002 0.01 520 1.5 1.5 0.0002 0.0106 530 1.5 1.5 0.0002 0.011540 1.5 1.5 0.0002 0.01105 550 1.5 1.5 0.0002 0.0115 560 1.5 1.5 0.00020.0126 570 1.5 1.5 0.0002 0.0136 580 1.5 1.5 0.0002 0.014 590 1.5 1.50.0002 0.0146 600 1.5 1.5 0.0002 0.0147 610 1.5 1.5 0.0002 0.0148 6201.5 1.5 0.0002 0.0148 630 1.5 1.5 0.0002 0.0147 640 1.5 1.5 0.00020.0148 650 1.5 1.5 0.0002 0.0146 660 1.5 1.5 0.0002 0.0143 670 1.5 1.50.0002 0.014 680 1.5 1.5 0.0002 0.0135 690 1.5 1.5 0.00018 0.0125 7001.5 1.5 0.00018 0.0124 710 1.5 1.5 0.00018 0.012 720 1.5 1.5 0.000180.011 730 1.5 1.5 0.00018 0.0105 740 1.5 1.5 0.00018 0.0102 750 1.5 1.50.00016 0.01 760 1.5 1.5 0.00015 0.0096 770 1.5 1.5 0.00014 0.0092 7801.5 1.5 0.00012 0.009

TABLE 3 wavelength birefringence (nm) Δn 380 0.1095635 390 0.107924 4000.1064565 410 0.105138 420 0.1039495 430 0.102876 440 0.1019025 4500.1010175 460 0.100212 470 0.0994755 480 0.098801 490 0.0981815 5000.0976125 510 0.0970875 520 0.0966025 530 0.0961545 540 0.095739 5500.0953525 560 0.094994 570 0.094659 580 0.094347 590 0.094055 6000.0937825 610 0.0935265 620 0.093286 630 0.0930605 640 0.0928485 6500.092649 660 0.0924605 670 0.092282 680 0.092114 690 0.091955 7000.0918045 710 0.091661 720 0.0915255 730 0.0913975 740 0.091275 7500.0911585 760 0.0910475 770 0.0909425 780 0.0908415

TABLE 4 anisotropy of dielectric constant Δe 5.0 elastic constant K11 12pN elastic constant K22 6 pN elastic constant K33 17 pN rubbingdirection of backlight side 315 degrees direction rubbing direction ofviewing side 45 degrees direction pretilt angle of backlight side 5degrees pretilt angle of viewing side 5 degrees chiral reagent nonethickness of cell 4 mm

TABLE 5 Δn_(xy) × d 0 nm in all wavelength region Δn_(xz) × d 92.4 nm inall wavelength region arrangement of retardation film A2 z axis with 45degree of backlight side tilt towered direction opposite to pretilt ofliquid crystal on backlight side arrangement of retardation film A1 zaxis with 45 degree of viewing side tilt towered direction opposite topretilt of liquid crystal on viewing side

TABLE 6 Δn_(xy) × d 0 nm in all wavelength region Δn_(xz) × d 73.92 nmin all wavelength region arrangement of retardation film B2 z axisdirection arranged of backlight side vertically with respect to grasssubstrate arrangement of retardation film B1 z axis direction arrangedof viewing side vertically with respect to grass substrate

FIG. 33 shows results of the contrast ratio of the polarizer 1 on theviewing side when turned with a wavelength of 550 nm.

From FIG. 33, it is found that, when the angle of the absorption axis ofthe polarizer 1 on the viewing side is 40.6 degrees, the highestcontrast ratio is obtained and the angle of the absorption axis deviatesfrom the 45 degrees of a crossed Nicols state with the polarizer on thebacklight side by 4.4 degrees.

Next wavelength dependency of the contrast ratio was calculated.Structure A of FIG. 34( a) is a structure in which the absorption axisof the polarizer 1 on the viewing side in the structure of FIG. 32 isarranged at an angle of 40.6 degrees. Structure B of FIG. 34( b) is astructure in which the absorption axis of the polarizer 1 on the viewingside in the structure A forms an angle of 45 degrees with the polarizeron the backlight side in a crossed Nicols state. Structure C of FIG. 34(c) is a structure in which each polarizer used is the polarizer 1 andthe outermost polarizer 1 on the viewing side is arranged at an angle of40.6 degrees. FIG. 35 shows the wavelength distribution of theextinction coefficients of the polarizer 1 and the polarizer 2. It isshown that the extinction coefficient of the polarizer 1 is large in ashorter wavelength range and the extinction coefficient of the polarizer2 is small in a larger wavelength range. Note that the property valuesof the polarizers 1 and 2; the property values of the liquid crystal,the retardation plates A1, A2, B1, and B2; and arrangement thereof arethe same as in Table 1, Table 2, Table 3, Table 4, Table 5, and Table 6.

The results of the contrast ratios of the 0 V transmittance and 5 Vtransmittance on the viewing side in the structures A, B, and C areshown in FIG. 36, and the magnified view in the case of the wavelengthsfrom 400 nm to 600 nm is shown in FIG. 37. When the structure A and thestructure B are compared, the structure A in which the polarizing platesare stacked so as to deviate at a wavelength other than a longerwavelength range of 690 nm or more results in a higher contrast. Thus,it is found that the contrast can be increased by stacking polarizingplates so that the polarizing plates are deviated.

Further, when the structure A and the structure C are compared, in whichpolarizing plates are deviated and stacked, the structure A in whichpolarizers having different wavelength distributions of extinctioncoefficients from each other with respect to the absorption axes resultsin a higher contrast in a long wavelength region. This increases thecontrast ratio because the extinction coefficient of the polarizer 1 issmaller than that of the polarizer 2 in a long wavelength region, andthe structure A in which the polarizers 2 having a larger extinctioncoefficient in a long wavelength region are stacked results in lowertransmittance when displaying black (5 V) in a long wavelength region asin FIG. 35.

From the above result, polarizers, each of which has differentwavelength distributions of extinction coefficients with respect to theabsorption axis, are stacked, and the polarizer on the viewing sidedeviates from a crossed Nicols state with respect to the polarizer onthe backlight side, thereby the high contrast ratio can be obtained.

This application is based on Japanese Patent Application serial No.2006-023853 filed in Japan Patent Office on Jan. 31 in 2006, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising: a first light-transmitting substrate anda second light-transmitting substrate which are disposed to face eachother; a display element sandwiched between the first light-transmittingsubstrate or the second light-transmitting substrate; and a layerincluding stacked polarizers on an outer side of the firstlight-transmitting substrate or the second light-transmitting substrate,wherein the stacked polarizers have different wavelength distributionsof extinction coefficients from each other with respect to absorptionaxes, and the stacked polarizers are arranged so that their absorptionaxes are deviated from a parallel Nicols state.
 2. A display devicecomprising: a first light-transmitting substrate and a secondlight-transmitting substrate which are disposed to face each other; adisplay element sandwiched between the first light-transmittingsubstrate and the second light-transmitting substrate; and a layerincluding stacked polarizers on an outer side of the firstlight-transmitting substrate or the second light-transmitting substrate;and a retardation plate provided between the layer including the stackedpolarizers and the first light-transmitting substrate or the secondlight-transmitting substrate, wherein the stacked polarizers havedifferent wavelength distributions of extinction coefficients from eachother with respect to absorption axes, and the stacked polarizers arearranged so that their absorption axes are deviated from a parallelNicols state.
 3. A display device comprising: a first light-transmittingsubstrate and a second light-transmitting substrate which are disposedto face each other; a display element sandwiched between the firstlight-transmitting substrate and the second light-transmittingsubstrate; a first layer including first stacked polarizers on an outerside of the first light-transmitting substrate; a second layer includingsecond stacked polarizers on an outer side of the secondlight-transmitting substrate, wherein the first stacked polarizers havedifferent wavelength distributions of extinction coefficients from eachother with respect to absorption axes, the second stacked polarizershave different wavelength distributions of extinction coefficients fromeach other with respect to absorption axes, the first stacked polarizersare arranged so that their absorption axes are deviated from a parallelNicols state, and the second stacked polarizers are arranged so thattheir absorption axes are in a parallel Nicols state.
 4. A displaydevice comprising: a first light-transmitting substrate and a secondlight-transmitting substrate which are disposed to face each other; adisplay element sandwiched between the first light-transmittingsubstrate and the second light-transmitting substrate; a first layerincluding first stacked polarizers on an outer side of the firstlight-transmitting substrate; a second layer including second stackedpolarizers on an outer side of the second light-transmitting substrate;a first retardation plate between the first layer including the firststacked polarizers and the first light-transmitting substrate; a secondretardation plate between the second layer including the second stackedpolarizers and the second light-transmitting substrate, wherein thefirst stacked polarizers have different wavelength distributions ofextinction coefficients from each other with respect to absorption axes,the second stacked polarizers have different wavelength distributions ofextinction coefficients from each other with respect to absorption axes,the first stacked polarizers are arranged so that their absorption axesare deviated from a parallel Nicols state, and the second stackedpolarizers are arranged so that their absorption axes are in a parallelNicols state.
 5. A display device comprising: a first light-transmittingsubstrate and a second light-transmitting substrate which are disposedto face each other; a display element sandwiched between the firstlight-transmitting substrate and the second light-transmittingsubstrate; a first layer including first stacked polarizers on an outerside of the first light-transmitting substrate; and a second layerincluding second stacked polarizers on an outer side of the secondlight-transmitting substrate, wherein the first stacked polarizers havedifferent wavelength distributions of extinction coefficients from eachother with respect to absorption axes, the second stacked polarizershave different wavelength distributions of extinction coefficients fromeach other with respect to absorption axes, the first stacked polarizersare arranged so that their absorption axes are deviated from a parallelNicols state, the second stacked polarizers are arranged so that theirabsorption axes are in a parallel Nicols state, the first layerincluding the first stacked polarizers has a first polarizer and asecond polarizer which are sequentially stacked from the firstlight-transmitting substrate side, and the first stacked polarizers andthe second stacked polarizers are arranged so that their absorption axesare in a crossed Nicols state.
 6. A display device comprising: a firstlight-transmitting substrate and a second light-transmitting substratewhich are disposed to face each other; a display element sandwichedbetween the first light-transmitting substrate and the secondlight-transmitting substrate; a first layer including first stackedpolarizers on an outer side of the first light-transmitting substrate; asecond layer including second stacked polarizers on an outer side of thesecond light-transmitting substrate; a first retardation plate betweenthe first light-transmitting substrate and the first layer including thefirst stacked polarizers; a second retardation plate between the secondlight-transmitting substrate and the second layer including the secondstacked polarizers, wherein the first stacked polarizers have differentwavelength distributions of extinction coefficients from each other withrespect to absorption axes, the second stacked polarizers have differentwavelength distributions of extinction coefficients from each other withrespect to absorption axes, the first stacked polarizers are arranged sothat their absorption axes are deviated from a parallel Nicols state,the second stacked polarizers are arranged so that their absorption axesare in a parallel Nicols state, the first layer including the firststacked polarizers has a first polarizer and a second polarizer whichare sequentially stacked from the first light-transmitting substrateside, and the first stacked polarizers and the second stacked polarizersare arranged so that their absorption axes are in a crossed Nicolsstate.
 7. A display device according to claim 3, wherein the displaydevice further comprises a light source on an outer side of the secondstacked polarizers.
 8. A display device according to claim 4, whereinthe display device further comprises a light source on an outer side ofthe second stacked polarizers.
 9. A display device according to claim 5,wherein the display device further comprises a light source on an outerside of the second stacked polarizers.
 10. A display device according toclaim 6, wherein the display device further comprises a light source onan outer side of the second stacked polarizers.
 11. A display deviceaccording to claim 1, wherein the stacked polarizers are providedbetween a pair of protective layers.
 12. A display device according toclaim 2, wherein the stacked polarizers are provided between a pair ofprotective layers.
 13. A display device according to claim 3, whereinthe first stacked polarizers and the second stacked polarizers are eachprovided between a pair of protective layers.
 14. A display deviceaccording to claim 4, wherein the first stacked polarizers and thesecond stacked polarizers are each provided between a pair of protectivelayers.
 15. A display device according to claim 5, wherein the firststacked polarizers and the second stacked polarizers are each providedbetween a pair of protective layers.
 16. A display device according toclaim 6, wherein the first stacked polarizers and the second stackedpolarizers are each provided between a pair of protective layers.
 17. Adisplay device according to claim 1, wherein each polarizers is providedbetween a pair of protective layers in the layer including the stackedpolarizers.
 18. A display device according to claim 2, wherein eachpolarizers is provided between a pair of protective layers in the layerincluding the stacked polarizers.
 19. A display device according toclaim 3, wherein each polarizer is provided between a pair of protectivelayers in the first layer and the second layers.
 20. A display deviceaccording to claim 4, wherein each polarizer is provided between a pairof protective layers in the first layer and the second layers.
 21. Adisplay device according to claim 5, wherein each polarizer is providedbetween a pair of protective layers in the first layer and the secondlayers.
 22. A display device according to claim 6, wherein eachpolarizer is provided between a pair of protective layers in the firstlayer and the second layers.
 23. A display device according to claim 1,wherein the display element is a liquid crystal element.
 24. A displaydevice according to claim 2, wherein the display element is a liquidcrystal element.
 25. A display device according to claim 3, wherein thedisplay element is a liquid crystal element.
 26. A display deviceaccording to claim 4, wherein the display element is a liquid crystalelement.
 27. A display device according to claim 5, wherein the displayelement is a liquid crystal element.
 28. A display device according toclaim 6, wherein the display element is a liquid crystal element.